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Salt tolerance in Zea mays (L). following inoculation with Rhizobium and Pseudomonas
Abstract
This study aimed to investigate the effect of inoculation with plant growth-promoting Rhizobium and Pseudomonas species on NaCl-affected maize. Two cultivars of maize (cv. Agaiti 2002 and cv. Av 4001) selected on the basis of their yield
potential were grown in pots outdoors under natural conditions during July. Microorganisms were applied at seedling stage
and salt stress was induced 21days after sowing and maintained up to 50% flowering after 120days of stress. The salt treatment
caused a detrimental effect on growth and development of plants. Co-inoculation resulted in some positive adaptative responses
of maize plants under salinity. The salt tolerance from inoculation was generally mediated by decreases in electrolyte leakage
and in osmotic potential, an increase in osmoregulant (proline) production, maintenance of relative water content of leaves,
and selective uptake of K ions. Generally, the microbial strain acted synergistically. However, under unstressed conditions,
Rhizobium was more effective than Pseudomonas but under salt stress the favorable effect was observed even if some exceptions were also observed. The maize cv. Agaiti
2002 appeared to be more responsive to inoculation and was relatively less tolerant to salt compared to that of cv. Av 4001.
... Proline is the main osmolyte produced by the hydrolysis of proteins in the plant under abiotic stress, reducing osmotic stress. However, proline is usually made and accumulated in plants under salt stress and plays a multifunctional role in regulating cytosolic acidity, maintaining protein and ROS, and aiding osmotic adjustments [325]. Applying proline led to elevated proline levels in plants experiencing salt stress, which correlated with enhanced salt tolerance [326]. ...
... increased the photosynthetic rate [363], Pseudomonas spp. Improved plant growth [325], Arthrobacter pascens decreased the Na accumulation. They increased plant growth [364], Azotobacter chroococcum improved nutrition [365], Rhizobium spp., Rhizobium tropici strain CIAT, Azotobacter brasilense strains Ab-V5 and Ab-V6 [366], and A. faecalis [367] enhanced the photosynthetic pigments and photosynthetic rate by the overproduction of proline in maize plants. ...
Maize, along with rice and wheat, is a popular staple food crop worldwide, and the most widely produced cereal crop. It is a versatile crop that may be utilized as a source of raw materials for human and animal fodders. Low agricultural yield and rapid population expansion significantly threaten future food security. Maize production is hampered by biotic and abiotic causes, with abiotic factors being the most critical limitation to agricultural output worldwide. Soil salinity is a key abiotic factor that reduces agricultural production by imposing negative impacts at several life cycle phases, including germination, seedling, vegetative, and reproductive development. Maize plants experience many physiological changes due to osmotic stress, toxicity of particular ions, and nutritional imbalance induced by salt stress. The degree and duration of stress, crop growth phases, genetic characteristics, and soil conditions influence yield reduction. Maize plants can tolerate salt stress involving a complex mechanism by changing their physiological, biochemical, and metabolic activities like stomatal functioning, photosynthesis, respiration, transpiration, hormone regulation, enzymes, metabolite generation, etc. After studying the salt tolerance mechanisms of maize plants under stress, integrated management techniques should be developed for maize agriculture in saline settings. Therefore, the study of plant responses to salt stress, stress tolerance mechanisms, and management strategies is one of the most imperative research fields in plant biology, and the study will focus on the effects of salt stress in different growth stages, plant tolerance mechanisms, and agronomic management practices for successful maize production all over the world.
... In this study, P. kurroa leaves also showed changes in response to the cold stress by increasing the synthesis of these osmoprotectants, as shown in Fig. 5. These regulatory proteins control and/or regulate the expression and activity of genes related to stress, hence contributing to cold stress tolerance (45). The increase in carbohydrates helps protect the structure of cell membranes, which plays an essential role in plant stress tolerance (46). ...
... A research report stated an accumulation of sucrose under cold stress (48). Bano and Fatima (2009) also observed a higher sugar concentration at high elevations. Researchers observed that the proline concentration significantly increases during cold hardening (49). ...
Plants growing at high elevations experience different environmental stresses, such as drought, salt, and cold. Among them, cold stress is the most prevalent one that affects the plants differently. Plants undergo biochemical, metabolic, molecular, and physiological changes under cold stress; hence, they adopt various mechanisms to tolerate it. The antioxidant defence system, osmotic regulators, and photosynthetic pigments in the plant provide them with stress tolerance. The present study is conducted on a high-altitude plant, Picrorhiza kurroa, which grows in such environmental conditions, to study the physiological parameters that provide a coping mechanism against cold stress. For this study, the leaves were collected from Pothivasa (2200 m.a.s.l) and Tungnath (3600 m.a.s.l) in Rudraprayag, Uttarakhand, India. The photosynthetic pigments (chlorophyll a, chlorophyll b, and carotenoids), lipid peroxidation, antioxidant enzymes, namely, superoxide dismutase, catalase, guaiacol peroxidase, ascorbate peroxidase, glutathione reductase, and osmoprotectants (protein, soluble sugar, and proline) present in the leaves were determined to visualize the impact of cold stress. It was revealed that the concentration of photosynthetic pigments increased with elevation. The activity of enzymes was analyzed, and they were observed to decrease with altitude. The malondialdehyde concentration, an indicator of lipid peroxidation, is higher in Pothivasa and lower in Tungnath. There is a significant increase in the osmoprotectants’ content along the altitudinal gradient. Therefore, the leaves from both sampling locations revealed the physiological changes that occurred in them to adapt to the cold stress conditions.
... Previous studies have reported that the increase of PGPR populations was effective on crops production under salt stress (Chatterjee et al., 2017). For instance, it was found that inoculation with PGPR can improve the nutritional status, antioxidant enzyme activity and growth of Zea mays under salt stress (Bano, Fatima, 2009). Other researchers indicated that PGPR inoculation improves salt tolerance in cucumber seedlings (Nadeem et al., 2016). ...
... Based on another study, Rizvi et al. (2022) revealed that IAA production by PGPR can improve plant growth under salt stress. Bano and Fatima (2009) reported that increased salt tolerance in Zea mays plants inoculated with PGPR resulted in an increase in the production of osmoregulant proline and selective K + uptake mechanisms. However, Rhizobium-inoculated plants grew better under non-saline conditions, while Pseudomonas exhibited more efficiency under salt stress. ...
... Similarly, high salt concentration reduces the uptake of crucial nutrients required for plant growth. Hence, plant growth is significantly retarded by salt stress, leading to low biomass accumulation and stunted development [7]. Stunted root growth and reduced leaf under high soil salinity result in reduced crop productivity [8]. ...
... Poor root growth, reduced leaf area and lower yield were recorded in the current study under salinity. It is well known that salinity impedes plant growth, resulting in reduced biomass accumulation [7]. The decreased crop yield and productivity under saline conditions can be attributed to stunted root growth and reduced leaf size [8]. ...
Salinity exerts significant negative impacts on growth and productivity of crop plants and numerous management practices are used to improve crop performance under saline environments. Micronutrients, plant growth promoting bacteria and biochar are known to improve crop productivity under stressful environments. Maize (Zea mays L.) is an important cereal crop and its productivity is adversely impacted by salinity. Although boron (B) application, seed inoculation with boron-tolerant bacteria (BTB) and biochar are known to improve maize growth under stressful environments, there is less information on their combined impact in enhancing maize productivity on saline soils. This study investigated the impact of B seed coating combined with seed inoculation with BTB + biochar on maize productivity under saline soil. Four B seed coating levels [0.0 (no seed coating), 1.0, 1.5, 2.0 g B kg⁻¹ seed], and individual or combined application of 5 % (w/w) maize stalk biochar, and seed inoculation with Bacillus sp. MN-54 BTB were included in the study. Different growth and yield attributes and grain quality were significantly improved by seed coating with 1.5 B kg⁻¹ seed coupled with biochar + BTB. Seed coating with 1.5 B kg⁻¹ seed combined with biochar + BTB improved stomatal conductance by 32 %, photosynthetic rate by 15 %, and transpiration ratio by 52 % compared to seed coating (0 B kg⁻¹ seed) combined with biochar only. Similarly, the highest plant height (189 cm), number of grain rows cob⁻¹ (15.5), grain yield (54.9 g plant⁻¹), biological yield (95.5 g plant⁻¹), and harvest index (57.6 %) were noted for B seed coating (1.5 g B kg⁻¹ seed) combined with biochar + BTB inoculation. The same treatment resulted in the highest grain protein and B contents. It is concluded that B seed coating at 1.5 g B kg⁻¹ seed combined with biochar + BTB inoculation could significantly improve yield and quality of maize crop on saline soils. However, further field experiments investigating the underlying mechanisms are needed to reach concrete conclusions and large-scale recommendations.
... Various environmental stresses such as flood, extreme temperatures, soil/water salinization, and drought impact the growth and development of plants and ultimately cause substantial decline in crop yield (Bano & Fatima, 2009;Jha et al., 2011). Under the ongoing climate changes, soil salinity is an expanding environmental issue, affecting millions of hectares of land around the world and resulting in enormous economic losses each year (Munns & Gilliham, 2015). ...
... In the last decade, a large number of reports documented that bacteria of various genera including Rhizobium, Bacillus, Pseudomonas, Azotobacter, Azospirillum, and Enterobacter conferred better behavior to their host plants against different abiotic stresses such as salinity (Egamberdieva et al., 2019;Etesami & Beattie, 2017;Etesami & Glick, 2020;Kumar et al., 2020;Sarkar et al., 2018). This PGPR capacity is notably ascribed to (i) the improvement of plant nutrition by increasing the solubilization of phosphorus and the potassium availability, biological nitrogen fixation, and iron sequestration, (ii) bacteria secretion of metabolic products (1-aminocyclopropane- (Bano & Fatima, 2009;Kohler et al., 2009;Kumar et al., 2018;Ullah et al., 2015). ...
Salinity is a widespread abiotic stress, which has strong adverse effects on plant growth and crop productivity. Exopolysaccharides (EPS) play a crucial role in plant growth‐promoting rhizobacteria (PGPR)‐mediated improvement of plant stress tolerance. This study aimed to assess whether Glutamicibacter sp. strain producing large amounts of EPS may promote tolerance of common reed, Phragmites australis (Cav.) Trin. ex Steud., towards salt stress. This halotolerant rizhobacterium showed tolerance to salinity (up to 1 M NaCl) when cultivated on Luria‐Bertani (LB) medium. Exposure to high salinity (300 mM NaCl) significantly impacted the plant growth parameters, but this adverse effect was mitigated following inoculation with Glutamicibacter sp., which triggered higher number of leaves and tillers, shoot fresh weight/dry weight, and root fresh weight as compared to non‐inoculated plants. Salt stress increased the accumulation of malondialdehyde (MDA), polyphenols, total soluble sugars (TSSs), and free proline in shoots. In comparison, the inoculation with Glutamicibacter sp. further increased shoot polyphenol content, while decreasing MDA and free proline contents. Besides, this bacterial strain increased tissue Ca ⁺ and K ⁺ content concomitant to lower shoot Na ⁺ and root Cl ⁻ accumulation, thus further highlighting the beneficial effect of Glutamicibacter sp. strain on the plant behavior under salinity. As a whole, our study provides strong arguments for a potential utilization of EPS‐producing bacteria as a useful microbial inoculant to alleviate the deleterious effects of salinity on plants.
... Nowadays, several studies have shown that microorganisms are involved in the tolerance of plants in extreme environments (Berríos et al. 2013;Gallardo-Cerda et al. 2018;Zhang et al. 2020). Several bacteria have been found in association with plant roots, including facilitating the establishment, spread, and/or increasing plant fitness in stressful environments (Bano and Fatima 2009;Hoffman and Arnold 2010;Turner et al. 2013;Torres-Diaz et al. 2016). The plant-microbe interactions occur mainly in two distinct rhizocompartments, the root endosphere and the rhizosphere (Turner et al. 2013). ...
Deschampsia antarctica Desv. and Poa annua L. are two Poaceae plants with enough endurance to successfully establish populations in the Antarctic region. Their adaptation to the Antarctic environment is closely linked to root-associated microbial communities. In this study, we obtained 16S rRNA sequencing data of the root-associated microbial communities of these two Poaceae plants from NCBI. Meta-analysis was used to investigate the similarities and differences between the root endosphere and rhizosphere-dwelling microbial communities in these two Poaceae plants. Here we report that two Poaceae-Poaceae plants’ rhizospheric communities were found to be more species diversity than endospheric communities. The species diversity of P. annua was higher than that of D. antarctica in both endosphere and rhizosphere communities. Seven bacterial families form a core microbiome of two Antarctic Poaceae plants’ root endosphere, in which Microbacteriaceae appears to be obligatory root endophytes of the two Antarctic Poaceae plants. The core microbiome of the two Poaceae plants’ rhizosphere has six bacterial families. Chitinophagaceae, Burkholderiaceae, and Flavobacteriaceae are most likely to play a crucial role in Poaceae plants’ adaptation to cold Antarctic conditions. Sphingobacteriaceae, Caulobacteraceae, Gemmatimonadaceae, and Flavobacteriaceae have a great influence on two Antarctic Poaceae plants.
... Organic osmoregulatory agents such as proline (Pro), soluble sugar, and glycine betaine (GB), play a pivotal role in preventing water loss in plants. Studies have shown a significant increase in the content of Pro and GB in maize under salt stress (Bano and Fatima, 2009). Additionally, the soluble sugar content of salt-tolerant maize lines has been reported to be higher than that of salt-sensitive lines. ...
Maize, a salt-sensitive crop, frequently suffers severe yield losses due to soil salinization. Enhancing salt tolerance in maize is crucial for maintaining yield stability. To address this, we developed an introgression line (IL76) through introgressive hybridization between maize wild relatives Zea perennis, Tripsacum dactyloides, and inbred Zheng58, utilizing the tri-species hybrid MTP as a genetic bridge. Previously, genetic variation analysis identified a polymorphic marker on Zm00001eb244520 (designated as ZmSC), which encodes a vesicle-sorting protein described as a salt-tolerant protein in the NCBI database. To characterize the identified polymorphic marker, we employed gene cloning and homologous cloning techniques. Gene cloning analysis revealed a non-synonymous mutation at the 1847th base of ZmSCIL76 , where a guanine-to-cytosine substitution resulted in the mutation of serine to threonine at the 119th amino acid sequence (using ZmSCZ58 as the reference sequence). Moreover, homologous cloning demonstrated that the variation site derived from Z. perennis. Functional analyses showed that transgenic Arabidopsis lines overexpressing ZmSCZ58 exhibited significant reductions in leaf number, root length, and pod number, alongside suppression of the expression of genes in the SOS and CDPK pathways associated with Ca²⁺ signaling. Similarly, fission yeast strains expressing ZmSCZ58 displayed inhibited growth. In contrast, the ZmSCIL76 allele from Z. perennis alleviated these negative effects in both Arabidopsis and yeast, with the lines overexpressing ZmSCIL76 exhibiting significantly higher abscisic acid (ABA) content compared to those overexpressing ZmSCZ58 . Our findings suggest that ZmSC negatively regulates salt tolerance in maize by suppressing downstream gene expression associated with Ca2+ signaling in the CDPK and SOS pathways. The ZmSCIL76 allele from Z. perennis, however, can mitigate this negative regulatory effect. These results provide valuable insights and genetic resources for future maize salt tolerance breeding programs.
... The ability of plants can be hampered to absorb water from the soil due to osmotic imbalance, which also causes toxicity of ions, deficiency of nutrients (N, Ca, K, P, Fe, Zn), and oxidative stress. Due to phosphate ions precipitating with Calcium ions in soils with high salinity, plant phosphorus (P) absorption is greatly decreased (Bano and Fatima, 2009). Some substances, including salt, chlorine, and boron, are specifically hazardous to plants. ...
... Salinity affects almost all aspects of plant development including germination, vegetative growth, and reproductive development. Soil salinity imposes ion toxicity, osmotic stress, nutrient deficiency (Bano & Fatima 2009); and increasing reactive oxygen species (ROS) production in chloroplasts (Talaat & Shawky 2013). Farooq et al. (2009) also mentioned that drought stress suppresses plant growth by affecting various physiological and biochemical processes, such as photosynthesis, respiration, translocation, ion uptake, carbohydrate metabolism, and nutrient uptake. ...
... In this study, two corresponding Pseudomonas isolates YE17 (resembling OTU2336) and XN05-1 were selected, and they significantly increased growth of salt-stressed wild soybean (Fig. 4). A variety of Pseudomonas species, e.g., P. stutzeri, P. koreensis and P. fluorescens, are potentially beneficial to host plants under salt stress [36][37][38][39] due to their significant properties in improving compatible solutes, antioxidant status, and plant growth 40,41 , all of which may result in their widespread occurrence in plants under stressful environments. It should be noted that strain XN05-1 shows the highest similarity with Stutzerimonas frequens (99.65%) and Stutzerimonas stutzeri (99.58%) now. ...
The root-associated microbiota plays an important role in the response to environmental stress. However, the underlying mechanisms controlling the interaction between salt-stressed plants and microbiota are poorly understood. Here, by focusing on a salt-tolerant plant wild soybean (Glycine soja), we demonstrate that highly conserved microbes dominated by Pseudomonas are enriched in the root and rhizosphere microbiota of salt-stressed plant. Two corresponding Pseudomonas isolates are confirmed to enhance the salt tolerance of wild soybean. Shotgun metagenomic and metatranscriptomic sequencing reveal that motility-associated genes, mainly chemotaxis and flagellar assembly, are significantly enriched and expressed in salt-treated samples. We further find that roots of salt stressed plants secreted purines, especially xanthine, which induce motility of the Pseudomonas isolates. Moreover, exogenous application for xanthine to non-stressed plants results in Pseudomonas enrichment, reproducing the microbiota shift in salt-stressed root. Finally, Pseudomonas mutant analysis shows that the motility related gene cheW is required for chemotaxis toward xanthine and for enhancing plant salt tolerance. Our study proposes that wild soybean recruits beneficial Pseudomonas species by exudating key metabolites (i.e., purine) against salt stress.
... In addition to this, inoculation of mustard plants with beneficial bacterial strain and/or MeJA singly or in combination further enhanced osmolytes concentration and maximally in combination. It has been reported that inoculation of plants with PGPR stimulates starch hydrolysis, releasing sugar for managing osmotic adjustments that lessen the impact of drought stress (Bano and Fatima 2009). Silva et al. (2020) also suggested that osmoprotectants enhanced with the inoculation of rhizobacterial strain to combat drought stress. ...
Drought stress poses a significant threat to crop productivity worldwide, necessitating innovative approaches to mitigate its adverse impact on crops. This study investigates the combined effects of methyl jasmonate and Pseudomonas fluorescens (P. fluorescens) under drought conditions in providing resilience to mustard plants (Brassica juncea) by bolstering antioxidative defense mechanisms, elevating secondary metabolite production, and promoting osmolyte accumulation. Under drought stress, mustard plants exhibited reduced growth and increased oxidative stress markers malondialdehyde and H2O2. However, the application of MeJA and P. fluorescens resulted in a substantial improvement in plant growth, as indicated by increased photosynthesis and shoots and root biomass with decrease in oxidative stress. This enhancement was attributed to an upregulation of antioxidative enzymes, including superoxide dismutase, catalase, and ascorbate peroxidase and glutathione reductase which collectively reduced reactive oxygen species levels and prevented oxidative damage. Furthermore, in combination they significantly enhanced the production of secondary metabolites and osmolytes enabling mustard plants to maintain cellular turgor and osmotic balance under drought conditions together with improved stress tolerance. In conclusion, these findings provide valuable insights into sustainable strategies for improving crop resilience to drought, with potential applications in agriculture to mitigate the adverse effects of climate change on crop production.
... The rhizobacteria (Bacillus subtilis and Bacillus pumilus) from soil showed PGPR functions, hydrogen cyanide and ammonia production, IAA production, tolerance to salt stress, and phosphate solubilization [148]. Bano and Fatima [149] showed that PGPB Pseudomonas and Rhizobium mitigate salinity-induced stress in Zea mays. Similarly, B. pumilus and P. pseudoalcaligenes reduce the activity of superoxide dismutase and lipid peroxidation in salinity-sensitive rice plants [150]. ...
Plant-microbe associations define a key interaction and have significant ecological and biotechnological perspectives. In recent times, plant-associated microbes from extreme environments have been extensively explored for their multifaceted benefits to plants and the environment, thereby gaining momentum in global research. Plant-associated extremophiles highlight ubiquitous occurrences, inhabiting extreme habitats and exhibiting enormous diversity. The remarkable capacity of extremophiles to exist in extreme environmental conditions is attributed to the evolution of adaptive mechanisms in these microbes at genetic and physiological levels. In addition, the plant-associated extremophiles have a major impact in promoting plant growth and development and conferring stress tolerance to the host plant, thereby contributing immensely to plant adaptation and survival in extreme conditions. Considering the major impact of plant-associated extremophiles from a socio-economic perspective, the article discusses their significance in emerging biotechnologies with a key focus on their ecological role and dynamic interaction with plants. Through this article, the authors aim to discuss and understand the favorable impact and dynamics of plant-associated extremophiles and their biotechnological utilities.
... Taking phosphorus from saline soil is difficult due to the precipitation of phosphate ions with calcium ions, rendering it inaccessible to plants [16]. By negatively impacting leguminous plants, which are susceptible to salinity, it decreases nitrogen in farming systems, resulting in a decrease in the use of synthetic nitrogen fertilizer [17]. ...
Nowadays, increased salt content in agricultural fields has become an acritical environmental concern, posing a threat to the human population worldwide regarding food security. Salinity can occur for several reasons, both natural and man-made. Natural soil salinization is caused by the weathering of high-salt-content rock minerals and sediments, fossil salt deposits, coastal land salinization, and salt transport in rivers. Anthropogenic activities result in salinization via improper irrigation, excessive groundwater extraction, land clearing for agriculture, the utilization of waste effluents, and excessive usage of chemical fertilizers. The freshwater supply is gradually dwindling and there is an urgent † Corresponding need for elucidation of the threat caused by salinity. Cultivating salt tolerance through classical breeding programmes is a much-preferred scientific purpose, but with modest success. Starting to introduce salt-tolerant microorganisms that increase crop development is another method for boosting crop salt tolerance. The salt-impacted region around the vicinity of plant roots provides a source of PGPR that can aid plants in adjusting to and growing in high-salinity conditions. Eco-friendly and plant growth is influenced by PGPR in direct and indirect ways with no detrimental effects on the environment. Direct mechanisms include phytohormone biosynthesis, siderophore, increased nitrogen fixation, and increased phosphate solubilization. Indirect mechanisms include phytopathogen inhibition, synthesis of antibiotics, siderophores, and ACC deaminase. By influencing elemental cycling as well as nutrient management, effective PGPR can help to manage salt stress, accelerate the production of crops, and diminish the use of fertilizers.
... Higher intensities of Cland Na + ions, as well as water intake, reduce N uptake in salty soils because Na + ions bind with NH 4 + and Clions bind with NO 3 -. Likewise, when (PO 4 ) 3 ion precipitates with Ca 2+ ions to create calcium phosphate, the plant's ability to take in P is diminished (Bano and Fatima 2009;Shrivastava and Kumar 2015). In contrast, elevated Na + ion concentrations drastically slow down the absorption of K + ions (Raddatz et al. 2020). ...
Agriculture accounts for approximately 11% of the total global GHG (greenhouse gases) emissions, and with the increase in emissions globally, efforts need to focus on improving farm management practices and the options used, more effectively and efficiently. Drought, rising temperatures, and greenhouse gas emissions all directly or indirectly impact human health and productivity of natural and agricultural ecosystems. The current farming practices also harm the food chain and ecosystem functioning. Applying beneficial microbial inoculants is one of the various techniques suggested to combat this widespread agricultural issue sustainably and mitigate the detrimental effects of the climate change. Beneficial microorganisms used as inoculants not only promote plant growth by addressing nutrient needs but also contribute significantly to manage environmental challenges. These microorganisms produce different types of substances such as extracellular polysaccharides (EPS), 1-aminocyclopropane-1-carboxylate (ACC) deaminase, siderophores, antioxidants, and volatile organic compounds (VOCs) that facilitate plants to negate the effects of climate change. This book chapter emphasizes the benefits of microbial inoculants and explores the mechanisms deployed in the mitigation of climate change on agricultural practices and balancing the ecosystem faction.
... Several studies have also revealed the biosynthesis of osmoprotectant trehalose by PGPR under saline conditions, which helps modulate plant defense responses (Shim et al., 2019). Similarly, co-inoculation of maize plants with Rhizobium and Pseudomonas resulted in increased salt tolerance through the selective uptake of K + ions, high levels of free proline, and decreased electrolyte leakage (Bano and Fatima 2009). Furthermore, under low salinity levels, the endophytic bacterium P. pseudoalcaligenes retained high levels of glycine-betaine, further enhancing plant resilience (Jha et al., 2011). ...
... It also results in nutritional imbalances. Soil sodicity significantly reduces phosphorus uptake by plants because phosphate ions precipitate with Ca ions (Bano and Fatima 2009). The enhanced Na absorption in sodic soils reduces K absorption which adversely affects the enzymatic activities involved in metabolic processes like photosynthesis and protein synthesis (Hauser and Horie 2010), which is detrimental for plant growth (Agarwal et al., 2005). ...
A field based survey was conducted for appraisal of salinity and sodicity problems of soils of Dhorimana and Gudhamalani tehsils of Barmer district of Rajasthan. Fifty seven composite surface soil samples (0-15 cm depth) were collected from the cultivated, irrigated fields during June, 2022 from thirty villages of Dhorimana and Gudhamalani tehsils. Twenty composite surface soil samples (0-15 cm depth) ten from each tehsil were also collected from adjacent cultivated, unirrigated fields on same time. The soil samples were analysed for various parameters by adopting standard methods and procedures. The majority of soils were belongs to sand to loamy sand in texture. Soils of the study area were found normal to alkaline in reaction, non saline and low in dehydrogenase activity. With respect to fertility, the organic carbon, available phosphorous and potassium were obtained low, low to medium and medium to high, respectively.
... Similarly, Kour et al. (2020) found that proline content doubled after inoculating wheat plants with Pseudomonas libanensis. Bano and Fatima (2009) reported that inoculating maize with Rhizobium and Pseudomonas SPP increased proline content and decreased electrolyte leakage, preserving the relative water content of the leaves. Kamali and Mehraban (2020) combined Nitroxin with Arbuscular Mycorrhizal fungi and inoculated sorghum under drought stress conditions, resulting in increased proline content and decreased electrolyte leakage. ...
Drought stress is one of the primary stresses that reduce crops’ yield in some parts of the world. In this regard, to mitigate drought stress effects on plants, farmers usually apply chemical fertilizers that lead to environmental issues. This study aimed to investigate the effect of biofertilizer application containing potassium-solubilizing bacteria (Pseudomonas koreensis and Pseudomonas vancouverensis), phosphorus-solubilizing bacteria (Pseudomonas putida), and nitrogen-fixing bacteria (Pantoea agglomerans) as an environmentally friendly biofertilizer for the growth and uptake of some essential nutrients in maize and its effect on drought tolerance. To achieve this, a Completely Randomized Design with ten treatments experiment was conducted in greenhouse conditions. The findings revealed that biofertilizers have the potential to improve maize yield and physiological characteristics, particularly under drought stress. The discussion section explores the mechanisms through which biofertilizers exert their effect and discusses practical implications for agricultural practices and environmental sustainability. Overall, this study contributes valuable insights into sustainable agricultural practices and has the potential to inform decision-making processes for farmers and policymakers.
... It might also be due to the retarded flow of sap flux that results in reduced root hydraulic conductivity with a possibility of lower leaf RWC 90 . However, improvement in the relative water content of stressed plants due to inoculation of rhizobia has been recorded by many researchers 87,88,91 . ...
Worldwide, salinity severely affects agricultural production of crops such as mung bean in arid and semi-arid regions. In saline conditions, various species of Rhizobium can be used to enhance nodulation and induce salinity tolerance in maize. The present study conducted a pot experiment to determine the efficiency of three rhizobial isolates under different salinity conditions, such as 1.41, 4 and 6 dS m ⁻¹ , on mung bean growth parameters, antioxidant status and yield. Results revealed that salt stress imparted adverse effects on the growth, antioxidants, yield and nodulation of mung bean. Under high salt stress conditions, fresh weights were reduced for roots (78.24%), shoots (64.52%), pods (58.26%) and height (32.33%) as compared to un-inoculated control plants. However, an increase in proline content (46.14%) was observed in high salt stressed plants. Three Rhizobium isolates (Mg1, Mg2, and Mg3), on the other hand, mitigated the negative effects of salt stress after inoculation. However, effects of Mg3 inoculation were prominent at 6 dS m ⁻¹ and it enhanced the plant height (45.10%), fresh weight of shoot (58.68%), root (63.64%), pods fresh weight (34.10%), pods number per plant (92.04%), and grain nitrogen concentration (21%) than un-inoculated control. Rhizobium strains Mg1, and Mg2 expressed splendid results at 1.41 and 4 dS m ⁻¹ salinity stress. The growth promotion effects might be due to improvement in mineral uptake and ionic balance that minimized the inhibitory effects caused by salinity stress. Thus, inoculating with these strains may boost mung bean growth and yield under salinity stress.
... The soil salinity may reduce overall economic revenues, productivity, and soil erosions (Bano and Fatima 2009;Hu and Schmidhalter 2004). The physico-chemical properties like pH, electrical conductivity, organic matter, and total nitrogen contents of bulk soil (BS) samples are presented in Table 1. ...
The most recent research has shown that the saline soil in Hyderabad, Sindh, Pakistan (southwestern Pakistan), was contaminated with trace and toxic metal concentrations above background levels. Therefore, the potential environmental hazards associated with the availability of Cd, Co, Cr, Cu, Pb, and Zn in this environment are of high ecological value. The mean values for Cd, Co, Cr, Cu, Pb, and Zn were found in the range of 1.01-3.26, 18.6-29.1, 5.07-13.6, 122-191, 4.01-9.99, and 170-193 μg/g in wetland metal-contaminated saline soil, respectively. The validation of the method was carried out by analysis of certified reference material; Community Bureau of Reference-483 (BCR-483) showed the percentage recovery > 98% in each case. The contamination factor (Cf), potential ecological risk factor (PERI), toxic response factor (Trf), degree of contamination (Dc), and potential ecological risk index (RI) showed that BS 1 and BS 3 contain more contamination of heavy metals. According to environmental risk analysis for heavy elements studies, the metal-polluted area of Hyderabad, Sindh, Pakistan, poses a high to moderate ecological danger.
... Soil microorganisms and metabolite−plant interactions have an important influence on the acquisition of high-yielding plant phenotypes [11]. Functional soil microorganisms promote plant growth through the production of plant growth hormones (e.g., glutathione and gibberellin), and which regulate root morphology and plant nutrient uptake, thereby directly increasing the plant growth rate and yield [12,13]. The production of antioxidants and stress proteins by the rhizosphere microbial community can help to increase plant stress tolerance [14], thus providing strong support for plants to cope with environmental stresses such as drought, salinity, pests, and diseases, and at the same time contribute to the establishment of rhizosphere homeostasis [15]. ...
Root−soil underground interactions mediated by soil microorganisms and metabolites are crucial for fertilizer utilization efficiency and crop growth regulation. This study employed a combined approach of soil microbial community profiling and non-targeted metabolomics to investigate the patterns of root-associated microbial aggregation and the mechanisms associated with metabolites under varying controlled-release fertilizer (CRF) application rates. The experimental treatments included five field application rates of CRF (D1: 675 kg/ha; D15: 1012.5 kg/ha; D2: 1350 kg/ha; D25: 1687.5 kg/ha; and D3: 2025 kg/ha) along with traditional fertilizer as a control (CK: 1687.5 kg/ha). The results indicated that the growth of sugarcane in the field was significantly influenced by the CRF application rate (p < 0.05). Compared with CK, the optimal field application of CRF was observed at D25, resulting in a 16.3% to 53.6% increase in sugarcane yield. Under the condition of reducing fertilizer application by 20%, D2 showed a 13.3% increase in stem yield and a 6.7% increase in sugar production. The bacterial ACE index exhibited significant differences between D25 and D1, while the Chao1 index showed significance among the D25, D1, and CK treatments. The dominant bacterial phyla in sugarcane rhizosphere aggregation included Proteobacteria, Acti-nobacteriota, and Acidobacteriota. Fungal phyla comprised Rozellomycota, Basidiomycota, and Ascomycota. The annotated metabolic pathways encompassed biosynthesis of secondary metabolites, carbohydrate metabolism, and lipid metabolism. Differential analysis and random forest selection identified distinctive biomarkers including Leotiomycetes, Cercospora, Anaeromyxobacter, isoleucyl-proline, and methylmalonic acid. Redundancy analysis unveiled soil pH, soil organic carbon, and available nitrogen as the primary drivers of microbial communities, while the metabolic profiles were notably influenced by the available potassium and phosphorus. The correlation heatmaps illustrated potential microbial−metabolite regulatory mechanisms under CRF application conditions. These findings underscore the significant potential of CRF in sugarcane field production, laying a theoretical foundation for sustainable development in the sugarcane industry.
... In the last decades, the use of salt-tolerant plant growth promoting rhizobacteria was associated to enhanced productivity and improvement of soil fertility in saline agriculture [37]. Under salinity stress, the co-inoculation of Rhizobium and Pseudomonas in corn (Zea mays) increased proline synthesis, maintaining the water level and selective uptake of ions, and decreased electrolyte leakage [38]. Another study showed that inoculation of chickpea with Rhizobium alleviates salt stress by increasing cell viability, stomatal movement, photosynthetic pigment and protein content, nitrate reductase, carbonic anhydrase, as well as enzymatic and non-enzymatic antioxidant activities [39]. ...
The rhizobia-Desmodium (Leguminosae, Papilionoideae) symbiosis is generally described by its specificity with alpha-rhizobia, especially with Bradyrhizobium. Our study aimed to isolate rhizobia from root nodules of native D. barbatum, D. incanum, and D. discolor, collected in remnants of the biomes of Atlantic Forest and Cerrado in protected areas of the Paraná State, southern Brazil. Based on the 16S rRNA phylogeny, 18 out of 29 isolates were classified as Alphaproteobacteria (Bradyrhizobium and Allorhizobium/Rhizobium) and 11 as Betaproteobacteria (Paraburkholderia). Phylogeny of the recA gene of the alpha-rhizobia resulted in ten main clades, of which two did not group with any described rhizobial species. In the 16S rRNA phylogeny of the beta-rhizobia, Paraburkholderia strains from the same host and conservation unity occupied the same clade. Phenotypic characterization of representative strains revealed the ability of Desmodium rhizobia to grow under stressful conditions such as high temperature, salinity, low pH conditions, and tolerance of heavy metals and xenobiotic compounds. Contrasting with previous reports, our results revealed that Brazilian native Desmodium can exploit symbiotic interactions with stress-tolerant strains of alpha- and beta-rhizobia. Stress tolerance can highly contribute to the ecological success of Desmodium in this phytogeographic region, possibly relating to its pioneering ability in Brazil. We propose Desmodium as a promising model for studies of plant-rhizobia interactions.
... Saline soil has a great effect on providing necessary elements for plants, causing soil toxicity and affecting the plants' absorption of elements. In addition, soil salinity can also affect the plants' ability to absorb water (Bano and Fatima 2009). In arid and semi-arid areas like Egypt, antitranspiration may reduce water consumption and improve water use efficiency (Singh et al 1999, Makus 1997. ...
... Boosting the antioxidative systems in plants for ROS (reactive oxygen species), scavenging, and production of polyamines and proline are also part of mechanisms employed by root-associated microbes for mitigating salt stress in plants. A Bano and M Fatima [65] induced salt stress conditions and coapplied Pseudomonas and Rhizobium at the seedling stage of maize. Their findings showed that under sodium chloride conditions alone, a harmful effect on maize growth and development was seen. ...
Plant roots host various microorganisms around and inside their roots, known as the root microbiome. To become healthy and productive, plants should keep under surveillance niches around the roots to recognize disease-causing microbes and similarly exploit the services of beneficial microorganisms in nutrient acquisition, stress mitigation and growth promotion. Here we presented the communication strategies between plant roots and root-associated microbes in improving plant growth and yield. Understanding how plant root and root-associated microbes communicate is vital in designing ecofriendly strategies for targeted disease suppression and improved plant growth that will help in sustainable agriculture.
... In comparison to control C0, the multi-strains significantly improved ionic balance in maize by controlling Na + and K + ions. Several microbial strains have been shown to reduce salt toxicity by balancing the Na + and K + levels [15,43,44]. In the current work, inoculating maize straw and seeds with multi-strain combinations dramatically increased N, P, and K levels in a saline medium (Table 4). ...
This study was undertaken to see how microbial consortia influenced maize development and yield under salt-affected conditions. The efficacy of the pre-isolated bacterial strains Burkholderia phytofirmans, Bacillus subtilis, Enterobacter aerogenes, and Pseudomonas syringae and Pseudomonas fluorescens to decrease the detrimental effects of salt on maize was tested in four distinct combinations using Randomized Complete Block Design with three replicates. The results revealed that these strains were compatible and collaborated synergistically, with an 80% co-aggregation percentage under salt-affected conditions. Following that, these strains were tested for their ability to increase maize growth and yield under salt-affected field conditions. The photosynthetic rate (11–50%), relative water content (10–34%), and grain yield (13–21%) of maize were all increased by these various combinations. However, when Burkholderia phytofirmans, Enterobacter aerogenes and Pseudomonas fluorescens were combined, the greatest increase was seen above the un-inoculated control. Furthermore, as compared to the un-inoculated control, the same combination resulted in a 1.5-fold increase in catalase and a 2.0-fold increase in ascorbate concentration. These findings showed that a multi-strain consortium might boost maize's total yield response as a result of better growth under salt stress.
... Soil salinity creates nutrient de ciency (including Ca, P, K, N, Fe and Zn), ion toxicity, osmotic and oxidative stress, and also bound the water uptake from the soil (Ashraf and Harris 2004; Ma et al. 2020). Excessive sodium limits phosphorous uptake and has toxic effects on the plants ( Bano and Fatima 2009;Shrivastava and Kumar 2015). Both ion toxicity and osmotic stress leads to the metabolite imbalance and hence results in oxidative stress (Chinnusamy et al. 2006) which involves rise in production of ROS (reactive oxygen species) including 1 . ...
Pea is the third most widely grown leguminous vegetable crop in the world. The crop is fairly easy to grow but is salt and drought sensitive limiting its yield. The current study was, therefore, designed to explore the morphological and biochemical responses of pea under salt stress and water-deficit stress. For this purpose, three pea varieties namely Climax, Green grass and Meteor were subjected to different levels (5.4 mM (Control), 50 mM, 75 mM and 100 mM of NaCl) of salt stress. The water-deficit stress was administered by watering 100%, 75% and 50% of field capacity. Morphological parameters showed significant reduction under salt stress and water-deficit stress in all the three varieties. On the other hand, the highest relative water content in response to various levels of both the stresses was 38.3% which was significantly lower than the control treatment. Chlorophyll content index (CCI), though, declined significantly in all the three varieties but Climax showed 43.7 CCI at 100 mM salt treatment which was significantly higher than Green grass (25.9 CCI) and Meteor (35.9 CCI) at same treatment. Significant accumulation of proline content was observed under both the stresses where 100 g of fresh weight of Climax showed proline content as 0.043 mg against 100 mM salt and 0.040 mg against 50% water-deficit treatments. Similar results were record for water-deficit stress study indicating common response of both kinds of stresses. The current findings may help understand better the contrasting impacts of salt and water scarcity stress on pea crops, specifically focusing on the role of proline.
Salinity, resulting from various contaminants, is a major concern to global crop cultivation. Soil salinity results in increased osmotic stress, oxidative stress, specific ion toxicity, nutrient deficiency in plants, groundwater contamination, and negative impacts on biogeochemical cycles. Leaching, the prevailing remediation method, is expensive, energy-intensive, demands more fresh water, and also causes nutrient loss which leads to infertile cropland and eutrophication of water bodies. Moreover, in soils co-contaminated with persistent organic pollutants, heavy metals, and textile dyes, leaching techniques may not be effective. It promotes the adoption of microbial remediation as an effective and eco-friendly method. Common microbes such as Pseudomonas, Trichoderma, and Bacillus often struggle to survive in high-saline conditions due to osmotic stress, ion imbalance, and protein denaturation. Halophiles, capable of withstanding high-saline conditions, exhibit a remarkable ability to utilize a broad spectrum of organic pollutants as carbon sources and restore the polluted environment. Furthermore, halophiles can enhance plant growth under stress conditions and produce vital bio-enzymes. Halophilic microorganisms can contribute to increasing soil microbial diversity, pollutant degradation, stabilizing soil structure, participating in nutrient dynamics, bio-geochemical cycles, enhancing soil fertility, and crop growth. This review provides an in-depth analysis of pollutant degradation, salt-tolerating mechanisms, and plant-soil-microbe interaction and offers a holistic perspective on their potential for soil restoration.
Beneficial microbes are crucial for improving crop adaptation and growth under vari-ous stresses. They enhance nutrient uptake, improve plant immune responses, and help plants tolerate stresses like drought, salinity, and heat. The yield potential of any crop is significantly influenced by its associated microbiomes and their potential to im-prove growth under different stressful environments. Therefore, it’s crucial and excit-ing to understand the mechanisms of plant-microbe interactions. Maize (Zea mays L.) is one of the primary staple foods worldwide, in addition to wheat and rice. Maize is also an industrial crop globally, contributing 83% of its production for use in feed, starch, and biofuel industries. Maize requires significant nitrogen fertilization to achieve opti-mal growth and yield. Maize plants are highly susceptible to heat, salinity, and drought stresses and require innovative methods to mitigate the harmful effects of environmental stresses and reduce the use of chemical fertilizers. This review summarizes our current understanding of the beneficial interactions between maize plants and specific microbes. These beneficial microbes improve plant resilience to stress and in-crease productivity. For example, they regulate electron transport, downregulate cata-ase, and upregulate antioxidants. We also review the roles of plant growth promoting rhizobacteria (PGPR) enhancing stress tolerance in maize. Additionally, we explore the application of these microbes in maize production and identify major knowledge gaps that need to be addressed to utilize the potential of beneficial microbes fully.
Plant growth-promoting rhizobacteria (PGPR) has been shown to govern a number of aspects of plant development, enabling the plant to survive and adapt to its surroundings, in response to unfavorable conditions that are abiotic in nature. As a staple crop, rice is particularly vulnerable to a variety of abiotic stresses including drought, salt, heavy metal toxicity, and high temperatures. In tandem, these stresses have a significant detrimental impact on rice productivity and quality. PGPR is a rhizosphere-dwelling microorganism that can improve plant development through a variety of distinctive methods, including nutrient uptake, phytohormone synthesis, modification of plant stress signaling pathways, and stimulation of stress-responsive genes. In this review, we studied the several abiotic pressures that are encountered and how PGPR can aid in resisting the stresses with a focus on rice crop, we additionally look at how PGPR minimize the dependency of agricultural soils on pesticides and chemical fertilizers. PGPR contributes to the long-term sustainability of ecosystems, plant productivity, and soil health by promoting environmentally friendly and sustainable farming practices.
Climatic changes and global warming produce abiotic stressors that affect plant development and productivity. Abiotic stressors, such as drought, salt, cold, and heat, significantly impair global agricultural crop yields. The endophyte is a type of endosymbiont, usually a bacteria or fungus that lives inside plant cells and doesn't cause disease in the host plant. This review scrutinizes the integral contribution of endophytes to augmenting abiotic stress tolerance in plants. The core analysis investigates the regulatory role and mechanism of endophytes in pivotal physiological aspects of plants under abiotic stress conditions. This includes their involvement in managing water uptake and maintaining water balance during drought and salinity stress, regulating osmotic stress, and scavenging reactive oxygen species (ROS). Additionally, the review explores and outlines diverse strategies for inoculating and applying endophytes to enhance abiotic stress tolerance in plants. Endophytes produce secondary active compounds that defend plants from diseases and extracellular enzymes that help endophytes colonize plant hosts. Microbial endophytes may help plants thrive in poor soil conditions through phytohormone production and hazardous chemical degradation. Endophytes use many processes to help plants survive drought, salt, nutritional deficiency, heavy metal stress, and temperature. These findings suggest that endophytes and rhizobacteria may help plants cope with abiotic stress. Still, more research is needed to understand the mechanisms and side effects that maximize their use in sustainable and climate-smart agriculture.
Sessile plants confront the fluctuating harsh environmental conditions and react to alterations in biotic and abiotic components of environments by symbiotic association between plant and biosphere. The origins of stresses are the vicinal environment, which is composed of biotic and abiotic agents. A wide range of molecular mechanisms are opted by the plants for their self-defense. The plant faces harsh conditions due to its molecular battery. Signaling molecules engineer the plants to tolerate the stresses. Transposable elements become active due to living and nonliving agents. Physical and chemical agents cause induction in mutation. These changes are the first driving step in the evolution of plants. During evolution, environmental changes force the plants to adapt or succumb to stress. The plants respond to the ecological conditions by modulating the gene programmer.
Molecular and Physiological Insights into Plant Stress Tolerance and Applications in Agriculture Part 2 is an edited volume that presents research on plant stress responses at both molecular and physiological levels. This volume builds on the previous volume to provide additional knowledge in studies on the subject.
Key Features
- Explains aspects of plant genetics central to research such as the role of cytosine methylation and demethylation in plant stress responses, and the importance of epigenetic genetics in regulating plant stress responses.
- Explores how Late Embryogenesis Abundant proteins affect plant cellular stress tolerance with an emphasis on their molecular mechanisms and potential implications.
- Focuses on beneficial microorganisms including rhizobacteria, endophytes, and mycorrhizal fungi, which are expected to be alternative fertilizers with the advantages of being cost-effective, toxin-free, and eco-friendly.
- Highlights the potential use of endophytic bacteria for protecting crops against pathogens
- Presents an in-depth analysis of the molecular level to understand the impact of ATP-binding cassette transporters on plant defense mechanisms with a discussion of the potential anti-pathogenic agents based on terpenes and terpenoids.
The content of the book is aimed at addressing UN SDG goals 2, 12, and 15 to achieve zero hunger and responsible consumption and production, and to sustainable use of terrestrial ecosystems, respectively.
This comprehensive resource is suitable for researchers, students, teachers, agriculturists, and readers in plant science, and allied disciplines.
While soybean ( Glycine max L.) provides the most important source of vegetable oil and protein, it is sensitive to salinity, which seriously endangers the yield and quality during soybean production. The application of Plant Growth‐Promoting Rhizobacteria (PGPR) to improve salt tolerance for plant is currently gaining increasing attention. Streptomycetes are a major group of PGPR. However, to date, few streptomycetes has been successfully developed and applied to promote salt tolerance in soybean. Here, we discovered a novel PGPR strain, Streptomyces lasalocidi JCM 3373 T , from 36 strains of streptomycetes via assays of their capacity to alleviate salt stress in soybean. Microscopic observation showed that S. lasalocidi JCM 3373 T does not colonise soybean roots. Chemical analysis confirmed that S. lasalocidi JCM 3373 T secretes indole‐3‐carboxaldehyde (ICA1d). Importantly, IAC1d inoculation alleviates salt stress in soybean and modulates its root architecture by regulating the expression of stress‐responsive genes GmVSP, GmPHD2 and GmWRKY54 and root growth‐related genes GmPIN1a, GmPIN2a, GmYUCCA5 and GmYUCCA6 . Taken together, the novel PGPR strain, S. lasalocidi JCM 3373 T , alleviates salt stress and improves root architecture in soybean by secreting ICA1d. Our findings provide novel clues for the development of new microbial inoculant and the improvement of crop productivity under salt stress.
Global soil salinization is becoming increasingly severe. Many excellent garden trees cannot be planted in coastal or saline-alkali parks. Traditional methods such as freshwater washing and deep tilling consume substantial financial and human resources; hence, it is a promising strategy to search for a biological alternative. Seventy-eight fungal endophytic strains were isolated from the roots of alive Acer buergerianum (trident maple). Through a salt-resistance test, a strain was found to improve the salt tolerance of the seedlings. We explored the mechanism of improvement of salt resistance of the seedlings with this isolate by determining the levels of compounds and enzyme activities associated with salt resistance of the seedlings. ACS53 was identified as a species of the genus Cylindrocarpon by morphological and molecular evaluation. This strain substantially increased the contents of abscisic acid (ABA), proline, and soluble sugar and the activities of superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD), which are related to stress tolerance, in seedlings under salt stress. The isolate also showed an ability to secrete abundant extracellular ABA, which may trigger salt tolerance of the seedlings. Biological methods are considered a potential strategy to cope with saline land. In this study, strain ACS53 belonging to the genus Cylindrocarpon was found to substantially improve the salt resistance of trident maple seedlings under salt stress. This may provide a potential sustainable method against salinization. It may also be helpful to better understand how a fungal endophyte improves the salt resistance of host plants.
Medicinal Plants: Microbial Interactions, Molecular Techniques, and Therapeutic Trends is a comprehensive exploration of the fascinating world of medicinal plants, their therapeutic advancements, and the application of molecular techniques to unlock their full potential. This book is structured into three illuminating sections, each shedding light on different facets of this rapidly developing field.
Section 1: Exploring Plant-Microbe Interactions
Covers the relationship between microbes and plants, the historical context and the pivotal role of microbes in shaping the future of medicinal plants. Discover the diverse array of bacteria associated with these plants and grasp their significance in enhancing the medicinal value of plants.
Section 2: Harnessing Molecular Techniques
Covers cutting-edge molecular techniques such as genome editing and modern breeding methods to optimize the genetic traits of medicinal plants. By understanding these techniques, readers will learn how to enhance plant growth, yield and quality.
Section 3: Nanotechnology for Therapeutic Enhancement
Covers nanotechnology and its transformative impact on medicinal plants. The section highlights emerging nano-engineering technology that can revolutionize the therapeutic properties of these plants.
Medicinal Plants: Microbial Interactions, Molecular Techniques, and Therapeutic Trends is a book for Interdisciplinary readers: students, scientists, academics, and industry professionals alike.
Whether you're a student, scientist, academic, or industry professional, this book is your gateway to the evolving world of plant-based medicine.
This volume is a compilation of reviews on the industrial usage of soil microorganisms. The contents include 16 brief reviews on different soil microbe assisted industrial processes. Readers will be updated about recent applications of soil bacteria, fungi and algae in sectors such as agriculture, biotechnology, environmental management.
The reviews also cover special topics like sustainable agriculture, biodiversity, ecology, and intellectual property rights of patented strains, giving a broad perspective on industrial applications of soil microbes.
Volume 2 includes reviews on destructive microbes like Macrophomina Phaseolina, eco-friendly microbes like Beauveria Bassiana, the identification of fungi in the rhizosphere, the industrial application of Trichoderma, and other topics. The text is easy to understand for readers of all levels, with references provided for the benefit of advanced readers.
Humankind interfered in the natural selection of plants in favor of traits such as yield, grain quality, productivity, and flavor principally at the expense of several biotic and abiotic stress tolerance capacities. Plants are subjected to the detrimental effects of the combination of these factors due to their stationary nature. Today, there are various breeding approaches from classical to transgenesis and even genome editing to tame plant genome for our purposes. Additionally, the significance of epigenetic regulation in response to biotic and abiotic stresses has been recognized in the last decade. Acquisition and preservation of stress memory for the progeny to allow them to adapt to similar conditions through methylation, histone modification, and chromatin structure alterations are the focus of attention. Enlightening the cross talk between these components of acquired transgenerational memory may aid to breed more efficient and environmentally friendly crops in current agricultural systems. Priming applications have been extensively studied to induce stress memory of the plant by external stimulus as a warning signal, which may ignite minor activations of stress-responsive gene expression and eventually turn into strong resistance. The present chapter will discuss the basis and the recent advances in plant epigenetic regulation with emphasis on chemical, biotic, and abiotic priming agents.
Soil salinization is a global issue that negatively impacts crop yield and has become a prime concern for researchers worldwide. Many important crop plants are susceptible to salinity-induced stresses, including ionic and osmotic stress. Approximately, 20% of the world's cultivated and 33% of irrigated land is affected by salt. While various agricultural practices have been successful in alleviating salinity stress, they can be costly and not environment-friendly. Therefore, there is a need for cost-effective and eco-friendly practices to improve soil health. One promising approach involves utilizing microbes found in the vicinity of plant roots to mitigate the effects of salinity stress and enhance plant growth as well as crop yield. By exploiting the salinity tolerance of plants and their associated rhizospheric microorganisms, which have plant growth-promoting properties, it is possible to reduce the adverse effects of salt stress on crop plants. The soil salinization is a common problem in the world, due to which we are unable to use the saline land. To make proper use of this land for different crops, microorganisms can play an important role. Looking at the increasing population of the world, this will be an appreciated effort to make the best use of the wasted land for food security. The updated information on this issue is needed. In this context, this article provides a concise review of the latest research on the use of salt-tolerant rhizospheric microorganisms to mitigate salinity stress in crop plants.
The world’s population is expected to reach nine billion by 2050 (FAO 2009), and the climate is also changing. Abiotic and biotic stresses are the major challenges in crop production worldwide, and climate change will likely lead to more severe abiotic and biotic stress conditions (Cobb et al. 2013). By the year 2050, 50% of all arable lands will be consequently threatened by global climate changes, low water availability, and salinization (Wang et al. 2003). Salinity and drought are the most severe abiotic stresses that threaten crop productivity worldwide (Guo et al. 2014). Drought is expected to increase in frequency and severity in the future due to climate change, mainly due to decreases in regional precipitation but also because of increasing evaporation driven by global warming (Lobell et al. 2008). Drought affects more than 10% of arable land, causing desertification, especially in arid and semiarid areas, while salinization is rapidly increasing on a global scale, declining average yields for most major crops (Bray et al. 2000). Soil salinization is one of the severe forms of soil degradation, which can arise from natural causes and human-mediated activity, such as irrigation in arid and semiarid regions (Rengasamy et al. 2010).
Endophytic microbes are plant-associated microorganisms that reside in the interior tissue of plants without causing damage to the host plant. Endophytic microbes can boost the availability of nutrient for plant by using a variety of mechanisms such as fixing nitrogen, solubilizing phosphorus, potassium, and zinc, and producing siderophores, ammonia, hydrogen cyanide, and phytohormones that help plant for growth and protection against various abiotic and biotic stresses. The microbial endophytes have attained the mechanism of producing various hydrolytic enzymes such as cellulase, pectinase, xylanase, amylase, gelatinase, and bioactive compounds for plant growth promotion and protection. The efficient plant growth promoting endophytic microbes could be used as an alternative of chemical fertilizers for agro-environmental sustainability. Endophytic microbes belong to different phyla including Euryarchaeota, Ascomycota, Basidiomycota, Mucoromycota, Firmicutes, Proteobacteria, and Actinobacteria. The most pre-dominant group of bacteria belongs to Proteobacteria including α-, β-, γ-, and δ-Proteobacteria. The least diversity of the endophytic microbes have been revealed from Bacteroidetes, Deinococcus-Thermus, and Acidobacteria. Among reported genera, Achromobacter, Burkholderia, Bacillus, Enterobacter, Herbaspirillum, Pseudomonas, Pantoea, Rhizobium, and Streptomyces were dominant in most host plants. The present review deals with plant endophytic diversity, mechanisms of plant growth promotion, protection, and their role for agro-environmental sustainability. In the future, application of endophytic microbes have potential role in enhancement of crop productivity and maintaining the soil health in sustainable manner.
Plant roots host numerous microorganisms around and inside their roots, forming a community known as the root microbiome. An increasing bulk of research is underlining the influences root-associated microbial communities can have on plant health and development. However, knowledge on how plant roots and their associated microbes interact to bring about crop growth and yield is limited. Here, we presented (i) the communication strategies between plant roots and root-associated microbes and (ii) the applications of plant root-associated microbes in enhancing plant growth and yield. This review has been divided into three main sections: communications between root microbiome and plant root; the mechanism employed by root-associated microbes; and the chemical communication mechanisms between plants and microbes and their application in plant growth and yield. Understanding how plant root and root-associated microbes communicate is vital in designing ecofriendly strategies for targeted disease suppression and improved plant growth that will help in sustainable agriculture. Ensuring that plants become healthy and productive entails keeping plants under surveillance around the roots to recognize disease-causing microbes and similarly exploit the services of beneficial microorganisms in nutrient acquisition, stress mitigation, and growth promotion.
Pea is a widely cultivated leguminous plant which also contributes to soil enrichment through nitrogen fixation and benefits crop rotations. However, large weed populations are a challenge for pea production, requiring effective management strategies. It is essential to highlight the influence of soil parameters, factors affecting the environment, and management practices on weed populations to develop effective weed control and maximize pea yield and ease of harvesting. In our study, a total of 31 pea fields were surveyed prior to harvest to determine the coverage of each weed species, with the aim of identifying the typical weeds in the study area. In addition, environmental, soil, and management factors were recorded for each field. Based on our hypotheses, these factors influence the weed composition, and these effects can be described by the dominance of weed species. In our study, summer annuals and geophytic perennials were common, with Echinochloa crus-galli and Convolvulus arvensis being most dominant. The analysis revealed that the year of data record, soil type, and farming system most significantly influenced weed composition. Weed species were observed to have varying responses to soil texture, salt concentration, and phosphorus content. The survey period, geographical factors, farming system, and tillage practices also played a role in determining weed flora. The findings suggest strong correlations between soil parameters and weed composition, highlighting the importance of soil management in weed control. The year of data collection had the greatest influence on weed infestation. Soil-related variables, such as soil type, also played a significant role. Farming systems had a smaller effect on weed composition. Comparing our results with previous country level weed surveys in Hungary, our results identified some unique characteristics in the weed flora of South-East Hungary.
Pot experiments were conducted to evaluate the effect of Rhizobium leguminosarum strains (TAL-377, TAL-379 and TAL-102) alone and in combination with Phosphorus on soybean. The parameters studied were survival of Rhizobium at pod filling stage and after harvesting, and root/ shoot dry and fresh weight of soybean under natural condition. Surface stererilized soybean seeds var. NARC-4 were sown in earthen pots filled with soil and sand 1:3. Phosphorus (P) was applied as single super phosphate (SSP) at the time of sowing in the soil. Soybean seeds were inoculated with Rhizobium strains as seed coating just before sowing. The effect of growth was highly significant (α0.05) with an increase in root/shoot dry and fresh weight in plants with mixture of Rhizobium inoculums with phosphorus on soybean. Among three strains TAL-102 performed well as compared to TAL-377 and 379 Rhizobium strains. The CFU count of Rhizobium and P solubilizing bacteria was found maximum both at pod filling and after harvesting stage when Rhizobium strains and P was applied in mixed culture. A mixture of effective strains with phosphorus is a promising way for enhancing the growth of legume crops.
The hypothesis that inoculation of transplants with vesicular-arbuscular mycorrhizal (VAM) fungi before planting into saline soils alleviates salt effects on growth and yield was tested on lettuce (Lactuca sativa L.) and onion ( Allium cepa L.). A second hypothesis was that fungi isolated from saline soil are more effective in counteracting salt effects than those from nonsaline soil. VAM fungi from high- and low-salt soils were trap-cultured, their propagules quantified and adjusted to a like number, and added to a pasteurized soil mix in which seedlings were grown for 3–4 weeks. Once the seedlings were colonized by VAM fungi, they were transplanted into salinized (NaCl) soil. Preinoculated lettuce transplants grown for 11 weeks in the saline soils had greater shoot mass compared with nonVAM plants at all salt levels [2 (control), 4, 8 and 12 dS m^−1] tested. Leaves of VAM lettuce at the highest salt level were significantly greener (more chlorophyll) than those of the nonVAM lettuce. NonVAM onions were stunted due to P deficiency in the soil, but inoculation with VAM fungi alleviated P deficiency and salinity effects; VAM onions were significantly larger at all salt levels than nonVAM onions. In a separate experiment, addition of P to salinized soil reduced the salt stress effect on nonVAM onions but to a lesser extent than by VAM inoculation. VAM fungi from the saline soil were not more effective in reducing growth inhibition by salt than those from the nonsaline site. Colonization of roots and length of soil hyphae produced by the VAM fungi decreased with increasing soil salt concentration. Results indicate that preinoculation of transplants with VAM fungi can help alleviate deleterious effects of saline soils on crop yield.
The aim of our work was to assess the growth and mineral nutrition of salt stressed Acacia auriculiformis A. Cunn. ex Benth. and Acacia mangium Willd. seedlings inoculated with a combination of selected microsymbionts (bradyrhizobia and mycorrhizal fungi). Plants were grown in greenhouse conditions in non-sterile soil, irrigated with a saline nutrient solution (0, 50 and 100 mM NaCl). The inoculation combinations consisted of the Bradyrhizobium strain Aust 13c for A. mangium and Aust 11c for A. auriculiformis, an arbuscular mycorrhizal fungus (Glomus intraradices, DAOM 181602) and an ectomycorrhizal fungus (Pisolithus albus, strain COI 007). The inoculation treatments were designed to identify the symbionts that might improve the salt tolerance of both Acacia species. The main effect of salinity was reduced tree growth in both acacias. However, it appeared that, compared with controls, both rhizobial and mycorrhizal inoculation improved the growth of the salt-stressed plants, while inoculation with the ectomycorrhizal fungus strain appeared to have a small effect on their growth and mineral nutrition levels. Endomycorrhizal inoculation combined with rhizobial inoculation usually gave good results. Analysis of foliar proline accumulation confirmed that dual inoculation gave the trees better tolerance to salt stress and suggested that the use of this dual inoculum might be beneficial for inoculation of both Acacia species in soils with moderate salt constraints.
Abstract
The aim of the present study was to isolate plant-beneficial bacteria (both Rhizobium and plant growth promoting rhizobacteria) from roots and nodules of chickpea (Cicer arietinum L.) and to study the effect of coinoculations on growth of two cultivars of chickpea. Four Rhizobium strains were obtained from roots and four from the nodules of field-grown chickpea cv. Parbat and identified on the basis of morphological characteristics, and biochemical and infectivity tests on the host seedlings. Only one type of nitrogen and carbon source utilisation pattern and DNA banding pattern of random amplified polymorphic DNA was observed in all isolates (Rn1, Rn2, Rn3, Rn4) from nodules, while two types of such patterns were detected among the isolates from roots. The isolate Rr1 from roots also exhibited a pattern identical to those of the isolates from nodules, whereas the remaining three isolates (Rr2, Rr3 and Rr4) from roots showed a different pattern. Two strains of plant growth-promoting rhizobacteria belonging to genus Enterobacter were also isolated from chickpea roots. All the Rhizobium strains and Enterobacter strains produced the plant growth hormones indole acetic acid and gibberellic acid in the growth medium. Effects of the bacterial isolates as single- or double-strain inocula were studied on two chickpea cultivars (NIFA 88 and Parbat) grown in sterilised soil. In cultivar NIFA 88, coinoculation of Rhizobium strain Rn1 with Enterobacter strain B resulted in maximum increase in plant biomass and nodulation, as compared with the control treatment (non-inoculated as well as inoculated with Rhizobium strain Rn1 only), whereas the combination of Rhizobium Rn1 with Enterobacter A was more efficient in growth promotion of chickpea cv. Parbat. In non-sterilised soil, the same combinations of the Rhizobium strain Rn1 with Enterobacter strains A and B were found to be the most effective inoculants for cvv. Parbat and NIFA 88, respectively. However, some negative effects on plant growth were also noted in cv. Parbat coinoculated with Rhizobium strain Rr2 and Enterobacter strain B.
High salt levels in soil and water can limit agricultural production and land development in arid and semiarid regions. Arbuscular mycorrhizal fungi (AMF) have been shown to decrease plant yield losses in saline soils. The objective of this study was to examine the growth and mineral acquisition responses of greenhouse-grown tomato to colonization by the AMF Glomus mosseae [(Nicol. And Gerd.) Gerd. and Trappe] under varied levels of salt. NaCl was added to soil in the irrigation water to give an ECe of 1.4 (control), 4.7 (medium) and 7.4 dS m(-1) thigh salt stress). Plants were grown in a sterilized, low P (silty clay) soil-sand mix. Mycorrhizal colonization was higher in the control than in saline soil conditions. Shoot and root dry matter yields and leaf area were higher in mycorrhizal than in nonmycorrhizal plants. Total accumulation of P, Zn, Cu. and Fe was higher in mycorrhizal than in nonmycorrhizal plants under both control and medium salt stress conditions. Shoot Na concentrations were lower in mycorrhizal than in nonmycorrhizal plants grown under saline soil conditions. The improved growth and nutrient acquisition in tomato demonstrate the potential of AMF colonization for protecting plants against salt stress in arid and semiarid areas.
The efficiency of 13 phosphate-solubilizing bacteria (PSB; four Burkholderia sp., five Enterobacter sp., and four Bradyrhizobium sp.) was assessed in a soil plate assay by evaluating soil phosphorus (P) availability. A commercial argentine strain, Pseudomonas
fluorescens, was used for comparing solubilizing activity. Burkholderia sp. PER2F, Enterobacter sp. PER3G, and Bradyrhizobium sp. PER2H strains solubilized the largest quantities of P in the soil plate assay after 60days as compared with the other
strains, including the commercial one. The effect of PSB inoculation on growth and nutrient uptake of soybean plants was also
studied under greenhouse conditions. Plants inoculated with Burkholderia sp. PER2F had the highest aerial height and showed an appropriate N/P ratio. However, none of the PSB increased P uptake
by plants. This suggests that PSB inoculation does not necessarily improve P nutrition in soybean, nor was there any relationship
between P availability in the soil plate assay and P content in the soybean shoot in the greenhouse. We concluded that the
selection of efficient PSB strains as possible inoculation tools for P-deficient soils should focus on the integral interpretation
of soil assays, greenhouse experiments, and field trials.
With the aim of determining whether the arbuscular mycorrhizal (AM) inoculation would give an advantage to overcome salinity
problems and if the phosphorus (P) concentration can profoundly influence zucchini (Cucurbita pepo L.) plant responses to AM, a greenhouse experiment was carried out with AM (+AM) and non-AM (−AM). Plants were grown in sand
culture with two levels of salinity (1 and 35mM NaCl, giving electrical conductivity values of 1.8 and 5.0dS m−1) and P (0.3 and 1mM P) concentrations. The percentages of marketable yield and shoot biomass reduction caused by salinity
were significantly lower in the plants grown at 0.3mM P, compared to those grown at 1mM P. However, even at high P concentration,
the absolute value of yield and shoot biomass of +AM zucchini plants grown under saline conditions was higher than those grown
at low P concentration. The +AM plants under saline conditions had higher leaf chlorophyll content and relative water content
than −AM. Mycorrhizal zucchini plants grown under saline conditions had a higher concentration of K and lower Na concentration
in leaf tissue compared to −AM plants. The P content of zucchini leaf tissue was similar for +AM and −AM treatments at both
low and high P concentrations in the saline nutrient solution. The beneficial effects of AM on zucchini plants could be due
to an improvement in water and nutritional status (high K and low Na accumulation).
A field experiment was conducted to examine the effect of the arbuscular mycorrhizal fungus Glomus macrocarpum and salinity on growth of Sesbania aegyptiaca and S. grandiflora. In the salt-stressed soil, mycorrhizal root colonisation and sporulation was significantly higher in AM-inoculated than in uninoculated plants. Mycorrhizal seedlings had significantly higher root and shoot dry biomass production than non-mycorrhizal seedlings grown in saline soil. The content of chlorophyll was greater in the leaves of mycorrhiza-inoculated as compared to uninoculated seedlings. The number of nodules was significantly higher in mycorrhizal than non-mycorrhizal plants. Mycorrhizal seedling tissue had significantly increased concentrations of P, N and Mg but lower Na concentration than non-mycorrhizal seedlings. Under salinity stress conditions both Sesbania sp. showed a high degree of dependence on mycorrhizae, increasing with the age of the plants. The reduction in Na uptake together with a concomitant increase in P, N and Mg absorption and high chlorophyll content in mycorrhizal plants may be important salt-alleviating mechanisms for plants growing in saline soil.
Rhizobium sp. strain WR1001, isolated from the Sonoran Desert by Eskew and Ting, was found to be able to grow in defined medium containing NaCl up to 500 mM, a concentration approaching that of sea water. Therefore, it is a valuable strain for studying the biochemical basis of salt tolerance. Intracellular free glutamate was found to increase rapidly in response to osmotic stress by NaCl. It accounted for 88% of the amino acid pool when the bacterium was grown in 500 mM NaCl. The role of glutamate dehydrogenase in glutamate biosynthesis was examined in several Rhizobium strains. Both NADH- and NADPH-dependent glutamate dehydrogenase activities in various Rhizobium strains were observed. The range of activity differed considerably depending on the particular strain. KCl (500 mM) did not stimulate glutamate dehydrogenase activity, as reported in a number of bacterial strains by Measures. The low activity of glutamate dehydrogenase in Rhizobium sp. strain WR1001 apparently cannot fulfill a biosynthetic function of glutamate formation in response to medium NaCl concentrations.
Salinity represents a serious threat to irrigated arable land. It has been estimated that about one-third of the irrigated land of the world is now salt-affected. In addition, vast areas of potentially fertile land cannot be used for the cultivation of conventional crops because of an excessive salt content of the soil.
Crop growth is not only depressed by excess salt but also by the poor quality of the structure of the saline soil. Under certain conditions chemical amendment (application of gypsum) may improve the physico-chemical quality of arable land but only locally and at high costs. For the arid and semi arid conditions in Pakistan it can be calculated that using the amount of water the river Indus transports through the flood plains, only a limited area can be properly irrigated and used for agriculture without salination. Therefore an extensive area of salt affected land will always remain and be abandoned by the farmers. During the last two decades biosaline research aims at cultivation of salt adapted plants on saline arable land.
The perspective of conventional screening and breeding techniques to obtain salt tolerant crops is discussed. Also advanced biotechnological approaches (callus and cell culture, meristem culture, plant regeneration, and protoplast fusion) have improved the possibilities to increase salt tolerance in plants. Fodderbeet is a domesticated cultivar of the coastal halophyte Beta vulgaris. Cultivars of the fodder beet were found fairly salt tolerant and even improved growth of the leaves and beet was found on saline land in field trials as compared with non-saline land.
Further field studies are being carried out to test the usefulness of this salt tolerant crop on salt affected land in Pakistan combined with other salt tolerant crops (Chenopods, grasses, legumes), to be used in rotation schemes. In addition, since the mechanism of salt tolerance is still incompletely understood, fundamental research is required to see how higher plants may grow well under saline conditions.
Relationship between salt tolerance and Ca^2+ retention among plant species was investigated using salt tolerant maize (Zea mays) and squash (Cucurbita maxima), and salt sensitive reed canarygrass (Phalaris arundinacea) and cucumber (Cucumis sativus). Ca^2+ was released extensively from root sections and intact roots of the salt sensitive plants by treatment with salt solutions. Distribution of Ca^2+ in shoot also decreased markedly in the salt sensitive plants by the treatment with the salt solutions. These results suggest that the ability of plants to retain Ca^2+ is associated with their salt tolerance.
Dual inoculation with VAM fungi and rhizobia isolates may help Leucaena leucocephala and Prosopis juliflora species mitigate the adverse effects of NaCl on juvenile growth and development. -from Authors
S ummary
Soil salinity decreased the Ca contents of shoots of two cultivars of barley ( Hordeum vulgare L.) grown under field conditions, particularly in younger leaves. Reduction in Ca content was more pronounced in cv. Arivat (the more salt‐sensitive cultivar) than in cv. Briggs. In seedlings grown in solution culture, relatively low concentrations of NaCl inhibited the transport of Ca to the shoot. This inhibition was not due to effects of NaCl on Ca influx into the root or on transpiration. We propose that NaCl inhibits Ca transport from root to shoot by interfering with the release of Ca into the root xylem, possibly via an effect on the active loading of Ca into xylem vessels.
Experiments have been carried out to determine the basis for the dependence of chloroplast pigment synthesis on protein synthesis in dark-grown cells of Euglena gracilis greening in the light. The complete inhibition of chlorophyll synthesis brought about by actidione (10 μg/ml) when added half way through the greening process was not relieved, even to the slightest extent, when 0.01 M δ-aminolaevulinic acid (ALA) was also present. The much smaller inhibition of chlorophyll synthesis brought about by chloramphenicol (2 mg/ml) was also relieved little, if at all, by the addition of ALA. It is concluded that the inhibition of chlorophyll synthesis by actidione can not be solely or primarily due to lack of ALA resulting from the decay of possibly labile enzymes of ALA synthesis, but could be due to inhibition of synthesis of the thylakoid structural protein. The results obtained with chloramphenicol are difficult to interpret because of the possibility that the drug, at high concentration, directly inhibits processes other than protein synthesis.
Chlorophyll and carotenoid synthesis by E. gracilis were both markedly stimulated by the addition of ALA. It is suggested that the rate of chlorophyll synthesis in the greening cells is limited by the rate of formation of ALA. The stimulation of formation of carotenoids as well as chlorophyll may indicate that the cells have a mechanism for ensuring that the rate of carotenoid synthesis does not fall below a certain proportion of the rate of chlorophyll synthesis.
A nomogram has been devised from which the concentrations of chlorophylls a and b, and total chlorophyll can be read off once the absorbances of an 80% acetone extract at 663 and 645 mμ have been determined.
The influence of NaCl on senescence-related parameters (protein and chlorophyll concentrations, membrane permeability and
chlorophyll fluorescence) was investigated in young and old leaves of five rice cultivars differing in salt resistance. NaCl
hastened the naturally-occurring senescence of rice leaves which normally appears during leaf ontogeny: it decreased chlorophyll
and protein concentrations and increased membrane permeability and malondialdehyde synthesis. Such an acceleration of deteriorative
processes affected all leaves in salt-sensitive cultivars while it was more marked in oldest than in youngest leaves of salt-resistant
genotypes. NaCl-induced senescence also involved specific modifications, such as an increase in basal non-variable chlorophyll
fluorescence (F 0) recorded in all cultivars or a transient increase in soluble protein concentration recorded in salt-resistant genotypes
only. Alteration of membrane permeability appeared as one of the first symptoms of senescence in rice leaves and allowed discrimination
among cultivars after only 7 d of stress. In contrast, F v/ F mratio (variable fluorescence/maximal fluorescence) was the same for all cultivars during the first 18 d of stress and thus
could not be used for identifying salt-resistant rice exposed to normal light conditions. Relationships between parameters
involved in leaf senescence are discussed in relation to salinity resistance of rice cultivars.
Plants colonized with arbuscular mycorrhizal (AM) fungi generally have greater growth and acquisition of mineral nutrients, and often have greater ability to withstand drought compared to nonmycorrhizal (nonAM) plants. This study determined effects of water stress (WS) versus no WS (nonWS) and the AM fungus Glomus monosporum (AM vs nonAM) on growth, acquisition of phosphorus (P), zinc (Zn), copper (Cu), manganese (Mn), and iron (Fe), and water use in two durum wheat (Triticum durum Desf.) cultivars exhibiting differences in resistance to WS. Plants were grown on soil [low P silty clay (Typic Xerochrept, pH=8.1)] and sand mixtures in a greenhouse. Shoot and root dry matter (DM), total root length (RL), and root colonization with AM for plants grown under non WS were higher than for plants grown under WS. Much of the reduction in DM was overcome by AM plants grown under WS. The ‘drought‐resistant’ wheat cultivar CR057 had higher AM root colonization than the ‘drought‐sensitive’ cultivar CR006 when grown with and without WS. Concentrations of P were lower and Zn, Cu, Mn, and Fe were higher in shoots of plants grown under WS compared to non WS. Nutrient contents were greater in AM than in nonAM plants, and these differences were greater under WS than under nonWS conditions. The AM plants had higher water use efficiency (WUE, g DM kg water evapotranspired) values than nonAM plants when grown under WS. The cultivar CR057 generally had higher WUE values than CR006. The results of this study indicated that AM plants had greater tolerance to drought stress than nonAM plants.
Accumulation of high levels of salts in the soil is characteristic of arid and semi-arid regions. Although different curative and management measures are being used to render salt-affected soils fit for agriculture, they are extremely expensive and do not provide permanent solutions to overcome the salinity problem. In contrast, a biotic approach for overcoming salinity stress has gained considerable recognition within the past few decades in view of the vast experimental evidence from what has happened in nature concerning the evolution of highly salt-tolerant ecotypes of different plant species, and also from the remarkable achievements that have been made in improveing different agronomic traits through artificial selection.
Referee: Dr. Lin Wu, Department of Environmental Horticulture, University of California, Davis, Davis, CA 95616 Cotton is a dual-purpose crop, widely used for fiber and oil purposes throughout the world. It is placed in the moderately salt-tolerant group of plant species with a salinity threshold level 7.7 dS m−1, its growth and seed yield being severely reduced at high salinity levels and different salts affect the cotton growth to a variable extent. However, inter- and intraspecific variation for cotton salt tolerance in cotton is considerable and thus can be exploited through specific selection and breeding for enhancing salt tolerance of the crop. There are contrasting reports regarding the crop response to salinity at different plant growth stages, but in most of them it is evident that the crop maintains its degree of salt tolerance consistently throughout its entire developmental phases. In the latter case an effective selection for salt tolerance is possible to be made at any growth stage of the crop. The pattern of uptake and accumulation of toxic ions (Na+ and/or Cl−) in tissues of plants subjected to saline conditions appears to be due mostly to the mechanism of partial ion exclusion (exclusion of Na+ and/or Cl−) in cotton. Maintenance of high tissue K/Na and Ca/Na ratios is suggested to be an important selection criterion for salt tolerance in cotton. While judging the appropriate mechanism of ion transport across the membranes in view of existing literature, it was evident that the PM-ATPase responds to increasing supply of Na+ in the growth medium, but the activity of the transport proteins on the plasma membrane alone were insufficient to regulate intracellular Na+ levels. Vacuolar-ATPase is also not responsive to increased external Na+. The inability of V-ATPase to respond to Na+ gave indication of the lack of effective driving force for compartmentalization of Na+ in cotton. However, in view of some latest studies concenrning the role of some antioxidants in salt tolerance of cotton it was suggested that high levels of antioxidants and an active ascorbate-glutathione cycle are associated with salt tolerance in cotton. Genetic studies with cotton in relation to salinity tolerance exhibited that most of growth, yield, and fiber characteristics are genetically based and most being QTL controlled and variable. The high additive component of variation can be exploited for breeding to produce further improvement in the salt tolerance of cotton.
The influence of NaCl on senescence-related parameters (protein and chlorophyll concentrations, membrane permeability and chlorophyll fluorescence) was investigated in young and old leaves of five rice cultivars diering in salt resistance. NaCl hastened the naturally-occurring senescence of rice leaves which normally appears during leaf ontogeny: it decreased chlorophyll and protein concentrations and increased membrane permeability and malondialdehyde synthesis. Such an acceleration of deteriorative processes aected all leaves in salt-sensitive cultivars while it was more marked in oldest than in youngest leaves of salt-resistant genotypes. NaCl-induced senescence also involved specific modifications, such as an increase in basal non-variable chlorophyll fluorescence (F ! ) recorded in all cultivars or a transient increase in soluble protein concentration recorded in salt-resistant genotypes only. Alteration of membrane permeability appeared as one of the first symptoms of senescence in rice leaves and allowed discrimination among cultivars after only 7 d of stress. In contrast, F v }F m ratio (variable fluorescence}maximal fluorescence) was the same for all cultivars during the first 18 d of stress and thus could not be used for identifying salt-resistant rice exposed to normal light conditions. Relationships between parameters involved in leaf senescence are discussed in relation to salinity resistance of rice cultivars. # 1996 Annals of Botany Company
Leaucaena leucocephala and Prosopis juliflora seedlings were grown in a sandy loam and loamy clay soil amended with three concentrations of NaCl with and without the mycorrhizal fungus Glomus fasciculatum and a Rhizobium isolate. After 16 weeks in glasshouse culture L. leucocephala and P. juliflora plants inoculated with G. fasciculatum and Rhizobium developed abundant vesicular‐arbuscular mycorrhizae (VAM) and root nodules in the sandy loam soil without NaCl amendments. In contrast, root system colonization by both rhizosphere symbionts was reduced in the loamy clay soil. In the absence of NaCl, plants inoculated with combinations of VAM and rhizobia had significantly greater total dry weight, tissue phosphorus concentration, and leaf area compared to seedlings colonized with individual symbionts in both soils. Although NaCl amendments greater than 40 and 80 mM decreased mycorrhizal colonization, number of chlamydospores, and root system nodulation by rhizobia, dry weight and tissue P concentration of plants colonized with VAM fungi and rhizobia were generally larger than those of seedlings colonized with only rhizobia. These data suggest that dual inoculation with VAM fungi and rhizobia isolates may help Leucaena and Prosopis species mitigate the adverse effects of NaCl on juvenile growth and development.
Maximum crop yields require sufficient phosphorus fertilization. Only phosphate in a soluble ionic form (Pi) is effective as a mineral nutrient. Current fertilizer technology supplies the soil solution with Pi via the application of large amounts of phosphate salts. Problems with this technology include energy-intensive production processes, the need for large scale mechanical application with associated environmental consequences, and reprecipitation of the phosphate into insoluble mineral complexes. It has been estimated that in some soils up to 75% of applied phosphate fertilizer may be lost to the plant because of mineral phase reprecipitation. Many approaches, ranging from cultural practices to biological inoculants such as mycorrhizal fungi, are being employed to enhance P-use efficiency. One area that is currently under-investigated is the ability of certain types of bacteria to solubilize mineral and organic phosphates. A review of the literature in the area of bacterial phosphate solubilization confirms that this trait is displayed by a wide range of bacteria. The phosphate starvation inducible (PSI) organic phosphate-solubilizing capability of E. coli is a component of a coordinately regulated gene system: the pho regulon. It has long been known that bacteria are also capable of solubilizing mineral phosphates such as hydroxyapatite. To date there has been no systematic study of the genetics of this phenomenon. Data from my laboratory indicate that the bacterial mineral phosphate-solubilizing (MPS) trait is regulated by the external level of Pi This conclusion is supported by results obtained from several types of molecular genetic studies. It is proposed that bacteria have mineral phosphate solubilizing (mps) genes. The potential agronomic applications of bacterial mineral and organic P solubilizing systems are discussed.
Three strains of Rhizobium able to fix nitrogen in symbiosis with lentils in saline soil were screened. Nodulation pattern, N2-fixation and grain yield were all influenced by Rhizobium strain and lentil genotype. Genotypes DL-443 and Pant L-406 were found to be more salt tolerant than others, and gave the highest grain yield.
Salt-stress effects on osmotic adjustment, ion and proline concentrations as well as proline metabolizing enzyme activities were studied in two rice (Oryza sativa L.) cultivars differing in salinity resistance: I Kong Pao (IKP; salt-sensitive) and Nona Bokra (salt-resistant). The salt-sensitive cultivar exposed to 50 and 100 mM NaCl in nutritive solution for 3 and 10 days accumulated higher levels of sodium and proline than the salt-resistant cultivar and displayed lower levels of osmotic adjustment. Proline accumulation was not related to proteolysis and could not be explained by stress-induced modifications in Δ1-pyrroline-5-carboxylate reductase (P5CR; EC 1.5.1.2) or proline dehydrogenase (PDH; EC 1.5.1.2) activities recorded in vitro. The extracted ornithine Δ-aminotransferase (OAT; EC 2.6.1.13) activity was increased by salt stress in the salt-sensitive cultivar only. In both genotypes, salt stress induced an increase in the aminating activity of root glutamate dehydrogenase (GDH; EC 1.4.1.2) while deaminating activity was reduced in the leaves of the salt-sensitive cultivar. The total extracted glutamine synthetase activity (GS; EC 6.3.1.2) was reduced in response to salinity but NaCl had contrasting effects on GS1 and GS2 isoforms in salt-sensitive IKP. Salinity increased the activity of ferredoxin-dependent glutamate synthase (Fd-GOGAT; EC 1.4.7.1) extracted from leaves of both genotypes and increased the activity of NADH-dependent glutamate synthase (NADH-GOGAT; EC 1.4.1.14) in the salt-sensitive cultivar. It is suggested that proline accumulation is a symptom of salt-stress injury in rice and that its accumulation in salt-sensitive plants results from an increase in OAT activity and an increase in the endogenous pool of its precursor glutamate. The physiological significance of the recorded changes are analyzed in relation to the functions of these enzymes in plant metabolism.
Soybean plants, varieties “Lee”, “Jackson” and “Bragg” were grown in solution culture at various salinity levels. A NaCl concentration of 10 mM was already inhibitory to growth of “Jackson”; growth of “Lee”, however, was only reduced at a salt concentration of 50 mM or higher. The moderately salt tolerant variety “Lee” efficiently excluded Cl ⁻ from the leaves up to about 50 mM NaCl in the medium, but showed high Cl ⁻ contents in the root; exclusion of Na ⁺ from the leaves was also apparent in this variety. On the other hand, the salt sensitive variety “Jackson” did not have the capacity for exclusion of Cl ⁻ and Na ⁺ . The physiological behaviour of the variety “Bragg” resembled that of “Jackson”.
It is suggested that the exclusion of Cl ⁻ and Na ⁺ from the leaves in the soybean variety “Lee” is regulated by the root.
Technological properties of wheat flours are largely governed by the functional properties of storage pro-teins, comprising single chain gliadins and disulphide-bonded polymeric proteins (glutenins, triticins, HMW albumins). This study was conducted (a) to measure the rate of accumulation of different classes of pro-teins, (b) to monitor the rate of polymerization of the polymeric subunits, and (c) to investigate the origin of differences in the degree of polymerization arising from allelic differences at the Glu-D1 locus of HMW glutenin subunits. Developing grains from hexaploid wheat cultivars were collected at 3-d intervals between 7 d and 40 d after anthesis (DAA). The accu-mulation behaviour of polymeric proteins was deter-mined by size exclusion-HPLC and of the constituent polypeptides (HMW glutenin subunits, LMW glutenin subunits, HMW albumin subunits) by a combination of SDS-PAGE, reversed phase-HPLC and immunoblot-ting. The relative time for peak accumulation of the albumins/gobulins, gliadins and polymeric proteins occurred in that order during grain filling. Deposition of HMW glutenin subunits, LMW glutenin subunits and HMW albumin subunits (^-amylases) began as early as 7 d after anthesis and progressed until maturity. Disulphide-linked aggregation (polymerization) of these subunits also commenced at 7 DAA. However, significant changes in size distribution of the polymers occurred only during the late stages of seed develop-ment which coincided with a rapid increase in the amounts of the glutenin subunits. The effects of HMW albumin subunits and LMW glutenin subunits on poly-mer size were relatively smaller than that of the HMW glutenin subunits. The wheat biotype with HMW glu-tenin subunits 5 + 10 {Glu-D1d allele) accumulated larger polymers more quickly than the biotype with allelic subunits 2 + 12 (Glu-D1a allele), this difference becoming apparent at 28 DAA which could be attrib-uted to variation in the accumulation rate of HMW glutenin subunits.
Four inbred maize lines differing in chilling tolerance were used to study changes in water status and abscisic acid (ABA) levels before, during and after a chilling period. Seedlings were raised in fertilized soil at 24/22°C (day/night), 70% relative humidity. and a 12-h photoperiod with 200 μmol m−2 s−1 from fluorescent tubes. At an age of 2 weeks the plants were conditioned at 14/12°C for 4 days and then chilled for 5 days at 5/3°C. The other conditions (relative humidity, quantum flux, photoperiod) were unchanged. After the chilling period the plants were transferred to the original conditions for recovery. The third leaves were used to study changes in leaf necrosis, ion efflux, transpiration, water status and ABA accumulation. Pronounced differences in chilling tolerance between the 4 lines as estimated by necrotic leaf areas, ion efflux and whole plant survival were observed. Conditioning significantly increased tolerance against chilling at 5/3°C in all genotypes. The genotypes with low chilling tolerance had lower water and osmotic potentials than the more tolerant genotypes during a chilling period at 5/3°C. These differences were related to higher transpiration rates and lower diffusive resistance values of the more susceptible lines. During chilling stress at 5/3°C ABA levels were quadrupled. Only a small rise was measurable during conditioning at 14/12°C. However, conditioning enhanced the rise of ABA during subsequent chilling. ABA accumulation in the two lines with a higher chilling tolerance was triggered at a higher leaf water potential and reached higher levels than in the less tolerant lines. We conclude that chilling tolerance in maize is related to the ability for fast and pronounced formation of ABA as a protective agent against chilling injury.
Native microflora present in the alkaline vertisols and two phosphate-solubilizing bacteria (PSB) isolated from soil using conventional screening media could not release phosphorus from alkaline Indian vertisol soils supplemented with carbon and nitrogen sources. The two PSBs could solubilize both rock phosphate and di-calcium phosphate in unbuffered media but failed to solubilize rock phosphate in buffered media. The organic acids secreted by these PSBs were 20–50 times less than that required to solubilize phosphorus from alkaline soil.
Proline, which increases proportionately faster than other amino acids in plants under water stress, has been suggested as an evaluating parameter for irrigation scheduling and for selecting drought-resistant varieties. The necessity to analyze numerous samples from multiple replications of field grown materials prompted the development of a simple, rapid colorimetric determination of proline. The method detected proline in the 0.1 to 36.0 moles/g range of fresh weight leaf material.
Two wheat (Triticum aestivum L.) genotypes differing in their sensitivity to water deficit (stress tolerant - C306 and stress susceptible - HD2329) were subjected to osmotic stress for 7 d using polyethylene glycol (PEG-6000; osmotic potential –1.0 MPa), at initial vegetative growth. The plants were either supplemented with 1 mM CaCl2 (Ca2+) alone or along with verapamil (VP; calcium channel blocker) to investigate the involvement of calcium in governing osmoregulation. Relative elongation rate (RER), dry matter (DM) production, water potential (w), electrolyte leakage (EL), contents of proline (Pro) and glycine betaine (GB) and activities of -glutamyl kinase (GK) and proline oxidase (PO) in shoots and roots were examined during stress period. C306 showed relatively higher accumulation of Pro while HD2329 accumulated more GB under stress. RER, DM and w were relatively higher in C306 than HD2329. Roots compared to shoots showed lower content of osmolytes but had faster rate of their accumulation. Presence of Ca2+ in the medium increased the activity of GK and decreased that of PO while in the presence of its inhibitor, decrease in activity of both the enzymes was observed. Ca2+ appeared to reduce the damaging effect of stress by elevating the content of Pro and GB, improving the water status and growth of seedlings and minimizing the injury to membranes. The protective effect of Ca2+ was observed to be more in HD2329 than C306.
Rhizobium Sp. UMKL 20 responded to increased sodium chloride concentration in the medium by elevating the intracellular concentrations of K+ and glutamate. Increases in K+ occurred in a time course synchronous with glutamate. Addition of the uncoupler 2,4-dinitrophenol, significantly reduced K+ uptake but had little effect on glutamate accumulation. New protein synthesis did not appear to be required for the stimulation of K+ uptake by NaCl. Assays of enzymes involved in glutamate synthesis showed that under salt-stress conditions, increased activities of glutamine synthetase and glutamate synthase were detected, indicating that the GS/GOGAT pathway is the major pathway for increasing intracellular glutamate concentration.
Large differences in N2-ase activity with fractions of active plants from 3–67% and maximal activities from 3–35 nmol C2H4.h-1 were found between sterile, Azospirillum-inoculated seedlings of 14 German cereal cultivars. Examples of similar cultivar differences in gnotobiotic or unsterile cereals in response to Azospirillum inoculation, in root exudation and the specificity of bacteria-root interactions are reviewed. As possible causes of yield responses to bacterial seed inoculation N2-fixation, plant growth regulating metabolites and bacterial interaction with root pathogens are discussed. The need for suitable screening methods to select and breed cultivars with desirable responses to beneficial rhizosphere bacteria is pointed out.
Root colonization and mitigation of NaCl stress on wheat seedlings were studied by inoculating seeds with Azospirillum lipoferum JA4ngfp15 tagged with the green fluorescent protein gene (gfp). Colonization of wheat roots under 80 and 160mM NaCl stress was similar to root colonization with this bacterial species under non-saline conditions, that is, single cells and small aggregates were mainly located in the root hair zone. These salt concentrations had significant inhibitory effects on development of seedlings, but not on growth in culture of gfp-A. lipoferum JA4ngfp15. Reduced plant growth (height and dry weight of leaves and roots) under continuous irrigation with 160mM NaCl was ameliorated by bacterial inoculation with gfp-A. lipoferum JA4ngfp15. Inoculation of plants subjected to continuous irrigation with 80mM NaCl or to a single application of either NaCl concentration (80 or 160mM NaCl) did not mitigate salt stress. This study indicates that, under high NaCl concentration, inoculation with modified A. lipoferum
reduced the deleterious effects of NaCl; colonization patterns on roots were unaffected and the genetic marker did not induce undesirable effects on the interaction between the bacterium and the plants.
Cell lines of a salt-sensitive cultivar of groundnut (Arachis hypogaea L. cv. JL24) were selected on media amended with high NaCl concentrations. Comparative analyses of the water status and ionic relations of salt-sensitive and salt-tolerant cell lines showed a decrease in the water potential (Nw) and solute potential (N?) with increases in salt stress. However, the maintenance of cellular turgor indicated active osmotic adjustments in response to salinity stress. In addition to the extrusion of Na+ in the NaCl-selected cell lines, a significant accumulation of proline was observed, which was probably associated with osmotic adjustments and the protection of membrane integrity. The addition of proline to the culture medium alleviated the salt stress-induced decline in fresh weight accumulation and reduced peroxidative damage to the lipid membranes, both in a concentration-dependent manner.
Seedlings of the rootstocks Pineapple sweet orange (SwO), Carrizo citrange (CC), and sour orange (SO) were grown in low phosphorus
(P) sandy soil and either inoculated with the vesicular-arbuscular mycorrhizal (VAM) fungus,Glomus intraradices, or were non-mycorrhizal (NM) and fertilized with P. VAM and NM seedings of similar shoot size and adequate P-status were
selected for study of salinity and flooding stress. One-third of each of the VAM and NM plants were given 150 mM NaCl for a period of 24 days. One-third of the plants were placed into plastic bags and flooded for 21 days while the remaining
third were non-stressed controls. In general, neither stress treatment affected mycorrhizal colonization. Salinity stress
reduced the hydraulic conductivity of roots, leaf water potential, stomatal conductance and net assimilation of CO2 (ACO2) of mycorrhizal and non-mycorrhizal seedlings to a similar extent. VAM plants of CC and SO accumulated more Cl in leaves
than NM plants. Cl was higher in non-mycorrhizal roots of SwO and CC than in mycorrhizal roots. Flooding the root zone for
3 weeks did not produce visible symptoms in the shoot but did influence plant water relations and reduce ACO2 of all 3 rootstocks. VAM and NM plants of each rootstock were affected similarly by flooding. Comparable reduction in nitrogen
and P content of both mycorrhizal and non-mycorrhizal plants suggested that flooding stress was primarily affecting root rather
than hyphal nutrient uptake.
The effect of salinity on the efficacy of two arbuscular mycorrhizal fungi, Glomus fasciculatum and G. macrocarpum, alone and in combination was investigated on growth, development and nutrition of Acacia auriculiformis. Plants were grown under different salinity levels imposed by 0.3, 0.5 and 1.0S m-1 solutions of 1M NaCl. Both mycorrhizal fungi protected the host plant against the detrimental effect of salinity. The extent of AM response on growth as well as root colonization varied with fungal species, and with the level of salinity. Maximum root colonization and spore production was observed with combined inoculation, which resulted in greater plant growth at all salinity levels. AM fungal inoculated plants showed significantly higher root and shoot weights. Greater nutrient acquisition, changes in root morphology, and electrical conductivity of soil in response to AM colonization was observed, and may be possible mechanisms to protect plants from salt stress.
The effect of salinity on some agro-physiological parameters in plants of five multigerm varieties of sugar beet has been investigated. Plants were submitted to four salt treatments, 0, 50, 100 and 200 mM NaCl, for 30 days in a sand culture and the physiological responses were measured. Salinity affected all of the considered parameters. Thus, high NaCl concentrations caused a great reduction in growth parameters such as leaf area, and fresh and dry weight of leaves and roots, but the leaf number was less affected. These changes were associated with a decrease in the relative water content and the K+ concentrations, but Na+ and Cl− contents were highly increased in the leaves. The solute leakage and proline content were also increased, but nitrate reductase activity was found to decrease in leaves of all of the tested varieties. Varietal differences were evident at the highest NaCl concentration for almost all of the considered parameters. The significance of inorganic ions and proline accumulation in relation to osmotic adjustment was discussed. In contrast to proline, inorganic ions seem to be involved in osmotic adjustment.
The relations between salinity and mineral nutrition of horticultural crops are extremely complex and a complete understanding of the intricate interactions involved would require the input from a multidisciplinary team of scientists. This review addresses the nutrient elements individually and we emphasise research directed towards the organ, whole-plant and field level. We have attempted to synthesise the literature and reconcile results from experiments conducted in a variety of conditions such as soil and solution cultures, those using mixed and single-salt (only NaCl) compositions, and those conducted over short (days) and long periods (months) of time.
Differences in osmoregulation were found in the leaves of closely related breeding lines and cultivars of chickpea (Cicer arietinum L.). Osmoregulation was determined from measurements of osmotic potentials (using thermocouple psychrometers) and relative water contents made on the leaves of plants grown in the glasshouse, and stressed by withholding water in a controlled-environment chamber.The controlled-environment measurements of osmoregulation were associated with increases in grain-yields in field experiments conducted at various sites in northern New South Wales in 1987 and 1988. The yield increases ranged from approximately zero in low-water-deficit environments (site mean yield, 3.5 t ha−1) to approximately 20% in high-water-deficit environments (site mean yield 1.3 t ha−1). These results suggest that osmoregulation may be a useful selection criterion in breeding for greater yields in water-limited environments.
Dry matter changes and ion partitioning in two near isogenic barley cultivars Maythorpe (relatively salt sensitive) and Golden Promise (relatively salt tolerant) were studied in response to increasing salinity. Although the growth of both cultivars was significantly reduced by exposure to NaCl, the effect was greater in Maythorpe, whilst Golden Promise maintained an increased ratio of young to old leaf blade. Golden Promise maintained significantly lower Na+ concentrations in young expanding tissues compared with Maythorpe. Partitioning of Cl– was evident in that both varieties maintained lower Cl– concentrations in mesophyll than in epidermal cells. Golden Promise maintained higher K+/Na+ and Ca2+/Na+ ratios in young leaf blade and young sheath tissues than Maythorpe when exposed to salt. Differences in ion partitioning and the maintenance of higher K+ and Ca2+ to Na+ ratios, especially in young growing and recently expanded tissues, would appear to be important mechanisms contributing to the improved salt tolerance of Golden Promise.
Thesis (Ph. D.)--University of Hawaii at Manoa, 1986. Bibliography: leaves 325-340. Photocopy. Microfiche. xxviii, 340 leaves, bound ill., maps 29 cm
Salt and drought stress signal transduction consists of ionic and osmotic homeostasis signaling pathways, detoxification (i.e., damage control and repair) response pathways, and pathways for growth regulation. The ionic aspect of salt stress is signaled via the SOS pathway where a calcium-responsive SOS3-SOS2 protein kinase complex controls the expression and activity of ion transporters such as SOS1. Osmotic stress activates several protein kinases including mitogen-activated kinases, which may mediate osmotic homeostasis and/or detoxification responses. A number of phospholipid systems are activated by osmotic stress, generating a diverse array of messenger molecules, some of which may function upstream of the osmotic stress-activated protein kinases. Abscisic acid biosynthesis is regulated by osmotic stress at multiple steps. Both ABA-dependent and -independent osmotic stress signaling first modify constitutively expressed transcription factors, leading to the expression of early response transcriptional activators, which then activate downstream stress tolerance effector genes.
Since 1922 when Wu proposed the use of the Folin phenol reagent for
the measurement of proteins (l), a number of modified analytical pro-
cedures ut.ilizing this reagent have been reported for the determination
of proteins in serum (2-G), in antigen-antibody precipitates (7-9), and
in insulin (10).
Although the reagent would seem to be recommended by its great sen-
sitivity and the simplicity of procedure possible with its use, it has not
found great favor for general biochemical purposes.
In the belief that this reagent, nevertheless, has considerable merit for
certain application, but that its peculiarities and limitations need to be
understood for its fullest exploitation, it has been studied with regard t.o
effects of variations in pH, time of reaction, and concentration of react-
ants, permissible levels of reagents commonly used in handling proteins,
and interfering subst.ances. Procedures are described for measuring pro-
tein in solution or after precipitation wit,h acids or other agents, and for
the determination of as little as 0.2 y of protein.
World population is increasing at an alarming rate and is expected to reach about six billion by the end of year 2050. On the other hand food productivity is decreasing due to the effect of various abiotic stresses; therefore minimizing these losses is a major area of concern for all nations to cope with the increasing food requirements. Cold, salinity and drought are among the major stresses, which adversely affect plants growth and productivity; hence it is important to develop stress tolerant crops. In general, low temperature mainly results in mechanical constraint, whereas salinity and drought exerts its malicious effect mainly by disrupting the ionic and osmotic equilibrium of the cell. It is now well known that the stress signal is first perceived at the membrane level by the receptors and then transduced in the cell to switch on the stress responsive genes for mediating stress tolerance. Understanding the mechanism of stress tolerance along with a plethora of genes involved in stress signaling network is important for crop improvement. Recently, some genes of calcium-signaling and nucleic acid pathways have been reported to be up-regulated in response to both cold and salinity stresses indicating the presence of cross talk between these pathways. In this review we have emphasized on various aspects of cold, salinity and drought stresses. Various factors pertaining to cold acclimation, promoter elements, and role of transcription factors in stress signaling pathway have been described. The role of calcium as an important signaling molecule in response to various stress signals has also been covered. In each of these stresses we have tried to address the issues, which significantly affect the gene expression in relation to plant physiology.