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Alleviation of gadolinium stress on Medicago by elevated atmospheric CO2 is mediated by changes in carbohydrates, Anthocyanin, and proline metabolism
Abstract
Rare earth elements (REE) like Gadolinium (Gd), are increasingly used in industry and agriculture and this is concomitant with the increasingly leaking of Gd into the environment. Under a certain threshold concentration, REE can promote plant growth, however, beyond this concentration, they exert negative effects on plant growth. Moreover, the effect of Gd on plants growth and metabolism under a futuristic climate with increasingly atmospheric CO2 has not yet been studied. To this end, we investigated the effect of soil contamination with Gd (150 mg/kg soil) on the growth, carbohydrates, proline, and anthocyanin metabolism of Medicago plants grown under ambient (aCO2, 410 ppm) or elevated CO2 (eCO2, 720 ppm) concentration. Gd negatively affected the growth and photosynthesis of plants and imposed oxidative stress i.e., increased H2O2 and lipid peroxidation (MDA) level. As defense lines, the level and metabolism of osmoprotectants (soluble sugars and proline) and antioxidants (phenolics, anthocyanins, and tocopherols) were increased under Gd treatment. High CO2 positively affected the growth and metabolism of Medicago plants. Moreover, eCO2 mitigated the negative impacts of Gd on Medicago growth. It further induced the levels of osmoprotectants and antioxidants. In line with increased proline and anthocyanins, their metabolic enzymes (e.g. OAT, P5CS, PAL, and CS) were also increased. This study advances our understanding of how Gd adversely affects Medicago plant growth and metabolism. It also sheds light on the biochemical mechanisms underlying the Gd stress-reducing impact of eCO2.
The increasing atmospheric CO2 concentration (e[CO2]) has mixed effects on soybean most varieties’ yield. This study elucidated the effect of e[CO2] on soybean yield and the underlying mechanisms related to photosynthetic capacity, non-structural carbohydrate (NSC) accumulation, and remobilisation. Four soybean cultivars were cultivated in open-top chambers at two CO2 levels. Photosynthesis rates were determined from R2 to R6. Plants were sampled at R5 and R8 to determine carbohydrate concentrations. There were significant variations in yield responses among the soybean cultivars under e[CO2], from no change in DS1 to a 22% increase in SN14. DS1 and SN14 had the smallest and largest increase, respectively, in daily carbon assimilation capacity. Under e[CO2], DS1, MF5, and XHJ had an increase in Ci, at which point the transition from Rubisco-limited to ribulose-1,5-bisphosphate regeneration-limited photosynthesis occurred, in contrast with SN14. Thus, the cultivars might have distinct mechanisms that enhance photosynthesis under e[CO2] conditions. A positive correlation was between daily carbon assimilation response to e[CO2] and soybean yield, emphasising the importance of enhanced photosynthate accumulation before the R5 stage in determining yield response to e[CO2]. E[CO2] significantly influenced NSC accumulation in vegetative organs at R5, with variation among cultivars. There was enhanced NSC remobilisation during seed filling, indicating cultivar-specific responses to the remobilisation of sucrose and soluble sugars, excluding sucrose and starch. A positive correlation was between leaf and stem NSC remobilisation and yield response to e[CO2], emphasising the role of genetic differences in carbohydrate remobilisation mechanisms in determining soybean yield variation under elevated CO2 levels.
Some radiological contrast agents have been shown to have effects on bacterial growth. In this study, the antibacterial effect and mechanism of action of iodinated X-ray contrast agents (Ultravist 370, Iopamiro 300, Telebrix Gastro 300 and Visipaque) and complexed lanthanide MRI contrast solutions (MultiHance and Dotarem) were tested against six different microorganisms. Bacteria with high and low concentrations were exposed to media containing different contrast media for various lengths of time and at pH 7.0 and 5.5. The antibacterial effect of the media was examined in further tests using agar disk diffusion analysis and the microdilution inhibition method. Bactericidal effects were found for microorganisms at low concentrations and low pH. Reductions were confirmed for Staphylococcus aureus and Escherichia coli.
For a long time, they have not received proper attention of researchers, whose interest was focused on other harmful environmental pollutants. However, the importance of REEs for modern technologies along with significant gaps in the knowledge about their effects on living organisms has changed the situation. Thanks to the active interest of researchers, a fairly large body of data on REEs in various areas has been accumulated, including their chemical and physical properties, their potential in engineering and instrumentation, their content in various natural objects, effects on human health, and interaction with other living organisms at the cellular level. This review analyzes and generalizes the new information about REEs as a relevant ecological factor with a special focus on the sources of REEs, specific features in their behavior in the soil, the effects of their interaction with plants, their manifestation, and putative mechanisms at the cellular level. The economic importance of plants to humans as well as their role for the entire biosphere as primary producers and their ability to be among the first ecosystem components that respond to negative changes requires focusing on these issues. The purpose of this review is to emphasize the research aspects that need a deeper insight, in particular, the soil–plant interaction and the effect of REEs on plant cell division.
Arsenic (As) contamination of soils limits agricultural productivity worldwide. The rise in atmospheric CO2 levels is predicted in the future climate. Elevated CO2 (eCO2) boosts plant growth both under optimal and environmental stress conditions. However, the interaction between eCO2 and heavy metals is rarely investigated at physiological and biochemical levels of different crop species groups such as C3 and C4. We tested the potential of eCO2 level (620 ppm) to alleviate the negative effects of soil As content (mild and severe treatments, 25 and 100 mg As/Kg soil) on growth, photosynthetic reactions and redox homeostasis in barley (C3) and maize (C4). Relative to maize plants, barley showed higher levels of As accumulation, particularly in their roots. As accumulation inhibited plant growth and differentially induced oxidative damage in barley and maize. Barley was found more susceptible to oxidative stress as observed by high H2O2 and protein oxidation contents. Interestingly, eCO2 differently mitigated As-induced oxidative stress in barley and maize. eCO2 markedly reduced the H2O2 production and alleviated lipid and protein oxidation in barely, and reduced As-induced increases in photorespiration (glycolate oxidase (GO) activity and glycine/serine (G/S) ratio). However, maize plants invested more on the antioxidant defense system to mitigate arsenic-induced oxidative stress as observed by significant increases in the contents of ascorbate-glutathione (ASC/GSH) cycle antioxidants. This work contributes to improving our understanding of the differences in growth, physiological and biochemical responses of major crops of two functional photosynthetic groups (C3 and C4 plants) under ambient and elevated CO2 grown under As stress.
Future climate CO2 (eCO2) and contamination with nano-sized heavy metals (HM-NPs) represent concurrent challenges threatening plants. The interaction between eCO2 and HM-NPs is rarely investigated, and no study has addressed their synchronous impact on the metabolism of the multifunctional stress-related metabolites, such as sugars and amino acids. Moreover, the characteristic responses of C3 and C4 plant systems to the concurrent impact of eCO2 and HM-NPs are poorly understood. Herein, we have assessed the impact of eCO2 (620 ppm) and/or HgO-NPs (100 mg/Kg soil) on growth, physiology and metabolism of sugars and amino acids, particularly proline, in C3 (wheat) and C4 (maize) plant systems. Under Hg-free conditions, eCO2 treatment markedly improved the growth and photosynthesis and induced sugars levels and metabolism (glucose, fructose, sucrose, starch, sucrose P synthase and starch synthase) in wheat (C3) only. In contrast, HgO-NPs induced the uptake, accumulation and translocation of Hg in wheat and to less extend in maize plants. Particularly in wheat, this induced significant decreases in growth and photosynthesis and increases in photorespiration, dark respiration and levels of tricarboxylic acid cycle organic acids. Interestingly, the co-application of eCO2 reduced the accumulation of Hg and recovered the HgO-NPs-induced effects on growth and metabolism in both plants. At stress defense level, HgO-NPs induced the accumulation of sucrose and proline, more in maize, via upregulation of sucrose P synthase, ornithine amino transferase, ∆¹-pyrroline-5-carboxylate (P5C) synthetase and P5C reductase. The co-existence of eCO2 favored reduced sucrose biosynthesis and induced proline catabolism, which provide high energy to resume plant growth. Overall, despite the difference in their response to eCO2 under normal conditions, eCO2 induced similar metabolic events in C3 and C4 plants under stressful conditions, which trigger stress recovery.
Salvia miltiorrhiza , known as danshen, is one of most valued medicinal plants in China. Although it has been cultivated since ancient times, an optimal culture system needs to be standardized for this important species. Here, we explored the phytochemical properties of S. miltiorrhiza with the treatments of rare earth elements (REEs) to develop an optimal tissue culture system. Four-week-old in vitro-grown S. miltiorrhiza plantlets were used as explants. The experiment was conducted in a randomized block design on a Murashige and Skoog (MS) medium containing 0.2 mg·L ⁻¹ naphthaleneacetic acid (NAA) to induce rooting at four different concentrations (50, 100, 200, and 300 μM) of REEs such as cerium (Ce), lanthanum (La), or praseodymium (Pr), respectively. Compared with all REEs at different concentrations, 100 μM Pr induced greater root length than Ce or La at any concentrations. Concomitantly, 0.38 μg tanshinone IIA/mg dry weight (DW) was observed, which was 54.84% higher than in the control. Similarly, chlorophyll content, antioxidant enzyme activity, and secondary metabolite were enhanced in rooting medium supplemented with 100 μM Pr. Therefore, this study showed that 100 μM Pr is an adequate concentration in the optimal culture system for promoting plant growth as well as enhancing secondary metabolite content in S. miltiorrhiza .
Aluminum (Al) toxicity is a major constraint for crop production in acid soils. Therefore, looking for sustainable solutions to increase plant tolerance to Al toxicity is needed. Although several studies addressed the potential utilization of silica or silicon dioxide nanoparticles (SNPs) to ameliorate heavy metal phytotoxicity, the exact mechanisms underlying SNPs-induced stress tolerance are still unknown. The current study investigated how SNPs could mitigate Al toxicity in maize plants grown on acidic soil. The impact of Al alone or in combination with SNPs on Al accumulation and detoxification, plant growth, photosynthetic C assimilation and redox homeostasis has been investigated. Al accumulation in stressed-maize organs reduced their growth, decreased photosynthesis related parameters and increased production of reactive oxygen species, through induced NADPH oxidase and photorespiration activities, and cell damage. These effects were more pronounced in roots than in leaves. SNPs ameliorated Al toxicity at growth, physiological and oxidative damage levels. Co-application of SNPs significantly reduced the activities of the photorespiratory enzymes and NADPH oxidase. It stimulated the antioxidant defense systems at enzymatic (superoxide dismutase, catalase, ascorbate and glutathione peroxidases) and non-enzymatic (ascorbate, glutathione, polyphenols, flavonoids, tocopherols, and FRAP) levels. Moreover, SNPs increased organic acids accumulation and metal detoxification (i.e. glutathione-S-transferase activity) in roots, as a protective mechanism against Al toxicity. The SNPs induced-protective mechanisms was dependent on the applied Al concentration and acted in organ-specific manner. Overall, the current study suggests the promising application of SNPs as an innovative approach to mitigate Al phytotoxicity in acidic soils and provides a comprehensive view of the cellular and biochemical mechanisms underlying this mitigation capacity.
Rare earth elements (REE) include the lanthanide series elements (La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu) plus Sc and Y. Currently these metals have become very critical to several modern technologies ranging from cell phones and televisions to LED light bulbs and wind turbines. This article summarizes the occurrence of these metals in the Earth's crust, their mineralogy, different types of deposits both on land and oceans from the standpoint of the new data with more examples from the Indian subcontinent. In addition to their utility to understand the formation of the major Earth reservoirs, multi-faceted updates on the applications of REE in agriculture and medicine including new emerging ones are presented. Environmental hazards including human health issues due to REE mining and large-scale dumping of e-waste containing significant concentrations of REE are summarized. New strategies for the future supply of REE including recent developments in the extraction of REE from coal fired ash and recycling from e-waste are presented. Recent developments in individual REE separation technologies in both metallurgical and recycling operations have been highlighted. An outline of the analytical methods for their precise and accurate determinations required in all these studies, such as, X-ray fluorescence spectrometry (XRF), laser induced breakdown spectroscopy (LIBS), instrumental neutron activation analysis (INAA), inductively coupled plasma optical emission spectrometry (ICP-OES), glow discharge mass spectrometry (GD-MS), inductively coupled plasma mass spectrometry (including ICP-MS, ICP-TOF-MS, HR-ICP-MS with laser ablation as well as solution nebulization) and other instrumental techniques, in different types of materials are presented. © 2019 China University of Geosciences (Beijing) and Peking University
The expression of stress related-genes against adverse environmental conditions has essential importance for plants. Tis study, using RT-qPCR, determined the expression of P5CS and PCS genes to investigate their roles in the leaves of tomato plants grown under heavy metal conditions. Te expression of the PCS1 gene is signifcantly induced under such conditions. Transcript expression of P5CS1, a gene responsible for proline synthesis, changed depending on
heavy metal doses; treatments of Cu (20 and 50 ppm), Cd and Pb (10 and 20 ppm) remarkably increased P5CS1 expression. However, the P5CS1 gene expression at 10 ppm dose of Cu and 50 ppm doses of Pb and Cd was not signifcantly different from that in control plants. Te metal-chelating potency of the extract of tomato leaves exposed to Pb and Cd was higher than that of untreated plants. Te proline content as assessed in the leaves of stressed plants was signifcantly
increased by applications of 10 and 20 ppm of Cd and Pb, and high doses of Cu. In addition, the results showed that the
proline content had a positive correlation with the P5CS1 gene expression in tomato leaves under application of these
tree heavy metals and that there was a positive relation between the PCS1 gene expression and metal-chelating ability of Cd-stressed plants.
Sucrose is the end product of photosynthesis and the primary sugar transported in the phloem of most plants. Sucrose synthase (SuSy) is a glycosyl transferase enzyme that plays a key role in sugar metabolism, primarily in sink tissues. SuSy catalyzes the reversible cleavage of sucrose into fructose and either uridine diphosphate glucose (UDP-G) or adenosine diphosphate glucose (ADP-G). The products of sucrose cleavage by SuSy are available for many metabolic pathways, such as energy production, primary-metabolite production, and the synthesis of complex carbohydrates. SuSy proteins are usually homotetramers with an average monomeric molecular weight of about 90 kD (about 800 amino acids long). Plant SuSy isozymes are mainly located in the cytosol or adjacent to plasma membrane, but some SuSy proteins are found in the cell wall, vacuoles, and mitochondria. Plant SUS gene families are usually small, containing between four to seven genes, with distinct exon-intron structures. Plant SUS genes are divided into three separate clades, which are present in both monocots and dicots. A comprehensive phylogenetic analysis indicates that a first SUS duplication event may have occurred before the divergence of the gymnosperms and angiosperms and a second duplication event probably occurred in a common angiosperm ancestor, leading to the existence of all three clades in both monocots and dicots. Plants with reduced SuSy activity have been shown to have reduced growth, reduced starch, cellulose or callose synthesis, reduced tolerance to anaerobic-stress conditions and altered shoot apical meristem function and leaf morphology. Plants overexpressing SUS have shown increased growth, increased xylem area and xylem cell-wall width, and increased cellulose and starch contents, making SUS high-potential candidate genes for the improvement of agricultural traits in crop plants. This review summarizes the current knowledge regarding plant SuSy, including newly discovered possible developmental roles for SuSy in meristem functioning that involve sugar and hormonal signaling.
Contents
Summary
32
I.
The importance of plant carbon metabolism for climate change
32
II.
Rising atmospheric CO2 and carbon metabolism
33
III.
Rising temperatures and carbon metabolism
37
IV.
Thermal acclimation responses of carbon metabolic processes can be best understood when studied together
38
V.
Will elevated CO2 offset warming‐induced changes in carbon metabolism?
40
VI.
No plant is an island: water and nutrient limitations define plant responses to climate drivers
41
VII.
Conclusions
42
Acknowledgements
42
References
42
Appendix A1
48
Summary
Plant carbon metabolism is impacted by rising CO2 concentrations and temperatures, but also feeds back onto the climate system to help determine the trajectory of future climate change. Here we review how photosynthesis, photorespiration and respiration are affected by increasing atmospheric CO2 concentrations and climate warming, both separately and in combination. We also compile data from the literature on plants grown at multiple temperatures, focusing on net CO2 assimilation rates and leaf dark respiration rates measured at the growth temperature (Agrowth and Rgrowth, respectively). Our analyses show that the ratio of Agrowth to Rgrowth is generally homeostatic across a wide range of species and growth temperatures, and that species that have reduced Agrowth at higher growth temperatures also tend to have reduced Rgrowth, while species that show stimulations in Agrowth under warming tend to have higher Rgrowth in the hotter environment. These results highlight the need to study these physiological processes together to better predict how vegetation carbon metabolism will respond to climate change.
Drought stress is one of the most important factors limiting the survival and growth of plants in different habitats of Egypt. This study was carried out to investigate the effect of drought stress on growth and some metabolic activities of sunflower seedlings under treatments with ascorbic acid (AsA) or CaCl2. Drought stress showed a marked reduction in shoot length, leaf area, shoot fresh and dry weight, photosynthetic pigments, soluble sugar, and amylase activity. On the other hand, root length, soluble proteins, protease activity, proline content, soluble phenolics and flavonoid contents, phenylalanine ammonia lyase(PAL), peroxidase (POX), polyphenol oxidase (PPO) activities, H2O2 and Malondialdehyde (MDA) contents,
and total antioxidant capacity were induced compared with normal plant. The application of AsA or CaCl2 mitigated the drought stress throughout the increase of growth criteria …
Concentrations of heavy metals in soil seldom reach a level sufficient to cause osmotic disturbances in plants. It is likely that water entry to the roots is indirectly governed by other factors which are themselves affected by metals. Decreased elongation of the primary root, impaired secondary growth, increased root dieback, or reduced root hair caused by toxic ions all exert a deleterious effect on the root-absorbing area and water uptake. Moreover, metals are able to decelerate short-distance water transfer both in symplast and apoplast, which in turn reduce the movement of water into the vascular system and affect water supply to the shoot. Long-distance transport is limited also due to decreased hydraulic conductivity in the root, stem and leaf midrib caused by a reduction in the size of vessels and tracheids, and partial blockage of xylem elements by cellular debris or gums. Heavy metals influence water delivery to the shoot due to inhibition of transpiration as they decrease the size of the leaves and the thickness of the lamina, reduce intercellular spaces, affect the density of stomata and decrease their aperture. Stomata closure is induced by direct interaction of toxic metals with guard cells and/or as a consequence of the early effects of metal toxicity on roots and stems. In metal-stressed plants, root-derived ABA or ABA-induced signals might play a role in stomatal movement. Disturbances in water relations trigger differential regulation of aquaporin gene expression, which may contribute to further reductions in water loss.
Background
Rising CO2 is expected to result in changes in plant traits that will increase plant productivity for some functional groups. Differential plant responses to elevated CO2 are likely to drive changes in competitive outcomes, with consequences for community structure and plant diversity. Many of the traits that are enhanced under elevated CO2 also confer competitive success to invasive species, and it is widely believed that invasive species will be more successful in high CO2. However, this is likely to depend on plant functional group, and evidence suggests that C3 plants tend to respond more strongly to CO2.
Results
We tested the hypothesis that invasive species would be more productive than noninvasive species under elevated CO2 and that stronger responses would be seen in C3 than C4 plants. We examined responses of 15 grass species (eight C3, seven C4), classified as noninvasive or invasive, to three levels of CO2 (390, 700 and 1000 ppm) in a closed chamber experiment. Elevated CO2 decreased conductance and %N and increased shoot biomass and C/N ratio across all species. Differences between invasive and noninvasive species depended on photosynthetic mechanism, with more differences for traits of C3 than C4 plants. Differences in trait means between invasive and noninvasive species tended to be similar across CO2 levels for many of the measured responses. However, noninvasive C3 grasses were more responsive than invasive C3 grasses in increasing tiller number and root biomass with elevated CO2, whereas noninvasive C4 grasses were more responsive than invasive C4 grasses in increasing shoot and root biomass with elevated CO2. For C3 grasses, these differences could be disadvantageous for noninvasive species under light competition, whereas for C4 grasses, noninvasive species may become better competitors with invasive species under increasing CO2.
Conclusions
The ecophysiological mechanisms underlying invasion success of C3 and C4 grasses may differ. However, given that the direction of trait differences between invasive and noninvasive grasses remained consistent under ambient and elevated CO2, our results provide evidence that increases in CO2 are unlikely to change dramatically the competitive hierarchy of grasses in these functional groups.
Electronic supplementary material
The online version of this article (doi:10.1186/s12898-016-0082-z) contains supplementary material, which is available to authorized users.
Elevated atmospheric CO2 can stimulate plant growth by providing additional C (fertilization effect), and is observed to mitigate abiotic stress impact. Although, the mechanisms underlying the stress mitigating effect are not yet clear, increased antioxidant defenses, have been held primarily responsible (antioxidant hypothesis). A systematic literature analysis, including “all” papers [Web of Science (WoS)-cited], addressing elevated CO2 effects on abiotic stress responses and antioxidants (105 papers), confirms the frequent occurrence of the stress mitigation effect. However, it also demonstrates that, in stress conditions, elevated CO2 is reported to increase antioxidants, only in about 22% of the observations (e.g., for polyphenols, peroxidases, superoxide dismutase, monodehydroascorbate reductase). In most observations, under stress and elevated CO2 the levels of key antioxidants and antioxidant enzymes are reported to remain unchanged (50%, e.g., ascorbate peroxidase, catalase, ascorbate), or even decreased (28%, e.g., glutathione peroxidase). Moreover, increases in antioxidants are not specific for a species group, growth facility, or stress type. It seems therefore unlikely that increased antioxidant defense is the major mechanism underlying CO2-mediated stress impact mitigation. Alternative processes, probably decreasing the oxidative challenge by reducing ROS production (e.g., photorespiration), are therefore likely to play important roles in elevated CO2 (relaxation hypothesis). Such parameters are however rarely investigated in connection with abiotic stress relief. Understanding the effect of elevated CO2 on plant growth and stress responses is imperative to understand the impact of climate changes on plant productivity.
It is well known that plant photosynthesis and respiration are two fundamental and crucial physiological processes, while the critical role of the antioxidant system in response to abiotic factors is still a focus point for investigating physiological stress. Although one key metabolic process and its response to climatic change have already been reported and reviewed, an integrative review, including several biological processes at multiple scales, has not been well reported. The current review will present a synthesis focusing on the underlying mechanisms in the responses to elevated CO2 at multiple scales, including molecular, cellular, biochemical, physiological, and individual aspects, particularly, for these biological processes under elevated CO2 with other key abiotic stresses, such as heat, drought, and ozone pollution, as well as nitrogen limitation. The present comprehensive review may add timely and substantial information about the topic in recent studies, while it presents what has been well established in previous reviews. First, an outline of the critical biological processes, and an overview of their roles in environmental regulation, is presented. Second, the research advances with regard to the individual subtopics are reviewed, including the response and adaptation of the photosynthetic capacity, respiration, and antioxidant system to CO2 enrichment alone, and its combination with other climatic change factors. Finally, the potential applications for plant responses at various levels to climate change are discussed. The above issue is currently of crucial concern worldwide, and this review may help in a better understanding of how plants deal with elevated CO2 using other mainstream abiotic factors, including molecular, cellular, biochemical, physiological, and whole individual processes, and the better management of the ecological environment, climate change, and sustainable development.
Date palm is an important crop, especially in the hot-arid regions of the world. Date palm fruits have high nutritional and therapeutic value and possess significant antibacterial and antifungal properties. In this study, we performed bioactivity analyses and metabolic profiling of date fruits of 12 cultivars from Saudi Arabia to assess their nutritional value. Our results showed that the date extracts from different cultivars have different free radical 13621 scavenging and anti-lipid peroxidation activities. Moreover, the cultivars showed significant differences in their chemical composition, e.g., the phenolic content (10.4–22.1 mg/100 g DW), amino acids (37–108 μmol·g −1 FW) and minerals (237–969 mg/100 g DW). Principal component analysis (PCA) showed a clear separation of the cultivars into four different groups. The first group consisted of the Sokary, Nabtit Ali cultivars, the second group of Khlas Al Kharj, Khla Al Qassim, Mabroom, Khlas Al Ahsa, the third group of Khals Elshiokh, Nabot Saif, Khodry, and the fourth group consisted of Ajwa Al Madinah, Saffawy, Rashodia, cultivars. Hierarchical cluster analysis (HCA) revealed clustering of date cultivars into two groups. The first cluster consisted of the Sokary, Rashodia and Nabtit Ali cultivars, and the second cluster contained all the other tested cultivars. These results indicate that date fruits have high nutritive value, and different cultivars have different chemical composition.
Anthocyanins are induced in plants in response to abiotic stresses such as drought, high salinity, excess light, and cold, where they often correlate with enhanced stress tolerance. Numerous roles have been proposed for anthocyanins induced during abiotic stresses including functioning as ROS scavengers, photoprotectants, and stress signals. We have recently found different profiles of anthocyanins in Arabidopsis (Arabidopsis thaliana) plants exposed to different abiotic stresses, suggesting that not all anthocyanins have the same function. Here, we discuss these findings in the context of other studies and show that anthocyanins induced in Arabidopsis in response to various abiotic stresses have different localizations at the organ and tissue levels. These studies provide a basis to clarify the role of particular anthocyanin species during abiotic stress.
The alarming and unprecedented rise in the atmo-spheric concentration of greenhouse gases under global climate change warrants an urgent need to understand the synergistic and holistic mechanisms associated with plant growth and productivity. Photosynthesis is a major process of sequestration and turnover of the total carbon on the planet. The extensive literature on the impacts of climate change demonstrates both posi-tive and negative effects of rising CO 2 on photosynthe-sis in different groups of higher plants. Significant variation exists in the physiological, biochemical and molecular responsiveness to elevated CO 2 atmosphere, among terrestrial plant species including those with C 3 , C 4 and crassulacean acid metabolic (CAM) path-ways. However, the regulatory events associated with the inter-and intraspecific metabolic plasticity gov-erned by genetic organization in different plants are little understood. The adaptive acclimation responses of plants to changing climate remain contradictory. This review focuses primarily on the impacts of global climate change on plant growth and productivity with special reference to adaptive photosynthetic acclima-tive responses to elevated CO 2 concentration. The effects of elevated CO 2 concentration on plant growth and development, source–sink balance as well as its interactive mechanisms with other environmental factors including water availability, temperature and mineral nutrition are discussed.
Elevated CO2 concentrations and extreme climate events, are two increasing components of the ongoing global climatic change factors, may alter plant chemical composition and thereby their economic and ecological characteristics, e.g. nutritional quality and decomposition rates. To investigate the impact of climate extremes on tissue quality, four temperate grassland species: the fructan accumulating grasses Lolium perenne, Poa pratensis, and the nitrogen (N) fixing legumes Medicago lupulina and Lotus corniculatus were subjected to water deficit at elevated temperature (+3°C), under ambient CO2 (392 ppm) and elevated CO2 (620 ppm). As a general observation, the effects of the climate extreme were larger and more ubiquitous in combination with elevated CO2. The imposed climate extreme increased non-structural carbohydrate and phenolics in all species, whereas it increased lignin in legumes and decreased tannins in grasses. However, there was no significant effect of climate extreme on structural carbohydrates, proteins, lipids and mineral contents and stoichiometric ratios. In combination with elevated CO2, climate extreme elicited larger increases in fructan and sucrose content in the grasses without affecting the total carbohydrate content, while it significantly increased total carbohydrates in legumes. The accumulation of carbohydrates in legumes was accompanied by higher activity of sucrose phosphate synthase, sucrose synthase and ADP-Glc pyrophosphorylase. In the legumes, elevated CO2 in combination with climate extreme reduced protein, phosphorus (P) and magnesium (Mg) contents and the total element:N ratio and it increased phenol, lignin, tannin, carbon (C), nitrogen (N) contents and C:N, C:P and N:P ratios. On the other hand, the tissue composition of the fructan accumulating grasses was not affected at this level, in line with recent views that fructans contribute to cellular homeostasis under stress. It is speculated that quality losses will be less prominent in grasses (fructan accumulators) than legumes under climate extreme and its combination with elevated CO2 conditions.
The effects of elevated CO2 (750 ppm vs. 390 ppm) were evaluated on nitrogen (N) acquisition and assimilation by three Medicago truncatula genotypes, including two N-fixing-deficient mutants (dnf1-1 and dnf1-2) and their wild-type (Jemalong). The proportion of N acquisition from atmosphere and soil were quantified by (15)N stable isotope, and N transportation and assimilation-related genes and enzymes were determined by qPCR and biochemical analysis. Elevated CO2 decreased nitrate uptake from soil in all three plant genotypes by down-regulating nitrate reductase (NR), nitrate transporter NRT1.1 and NR activity. Jemalong plant, however, produced more nodules, up-regulated N-fixation-related genes and enhanced percentage of N derived from fixation (%Ndf) to increase foliar N concentration and N content in whole plant (Ntotal Yield) to satisfy the requirement of larger biomass under elevated CO2. In contrast, both dnf1 mutants deficient in N fixation consequently decreased activity of glutamine synthetase/glutamate synthase (GS/GOGAT) and N concentration under elevated CO2. Our results suggest that elevated CO2 is likely to modify N acquisition of M. truncatula by simultaneously increasing N fixation and reducing nitrate uptake from soil. We propose that elevated CO2 causes legumes to rely more on N fixation than on N uptake from soil to satisfy N requirements.
The effect of light source and CO2 concentration on the growth and anthocyanin content of lettuce (Lactuca sativa L. ‘Seonhong Jeokchukmyeon’) grown in growth chambers was examined. The plant was grown under 140 μmol· m−2·s−1 PPF provided by either cool white fluorescent lamps (F, the control), white (W) light emitting diodes (LEDs), or a 8:1:1 mixture of red, blue and white (RBW) LEDs. Carbon dioxide concentration of the atmosphere was maintained at either 350, 700, or 1,000 μmol·mol−1. The RBW treatment promoted vegetative growth of the shoot and root. Chlorophyll fluorescence (Fv/Fm) was not significantly affected by the light source and CO2 concentration. Total anthocyanin content of the plant supplied with 1,000 mol·mol−1 CO2 was the greatest in the F treatment. Photosynthetic rate significantly increased with the increasing CO2 concentration. These results suggested that the RBW which provided a wider spectrum of PAR and the highest CO2 concentration provided the most the suitable environment condition for vegetative growth of lettuce among the tested light sources. To obtain plants with even higher quality, especially having greater content of anthocyanin, however, more considerations on supplemental light source including white LED are necessary in terms of optimum intensity, photoperiod, and optimum ratios of mixing with other LEDs.
The phytotoxicity of rare earth elements (REEs) is still poorly understood. The exposure-response relationships of three native Canadian plant species (common milkweed, Asclepias syriaca L., showy ticktrefoil, Desmodium canadense (L.) DC. and switchgrass, Panicum virgatum L.) and two commonly used crop species (radish, Raphanus sativus L., and tomato, Solanum lycopersicum L.) to the REEs lanthanum (La), yttrium (Y) and cerium (Ce) were tested. In separate experiments, seven to eight doses of each element were added to the soil prior to sowing seeds. Effects of REE dose on germination were established through measures of total percent germination and speed of germination; effects on growth were established through determination of above ground biomass. Ce was also tested at two pH levels and plant tissue analysis was conducted on pooled samples. Effects on germination were mostly observed with Ce at low pH. However, effects on growth were more pronounced, with detectable inhibition concentrations causing 10% and 25% reductions in biomass for the two native forb species (A. syriaca and D. canadense) with all REEs and on all species tested with Ce in both soil pH treatments. Concentration of Ce in aboveground biomass was lower than root Ce content, and followed the dose-response trend. From values measured in natural soils around the world, our results continue to support the notion that REEs are of limited toxicity and not considered extremely hazardous to the environment. However, in areas where REE contamination is likely, the slow accumulation of these elements in the environment could become problematic.
A mathematical model of the flavor thresholds of organic acids in beer as a function of their physical and chemical properties was constructed. Principal components analysis (PCA) was applied to 11 properties for 17 acids; this resulted in four significant principal components (PCs), which accounted for 93% of the variance in the property data. The PCs were dominated by the number of polar groups, the number of double bonds, molecular size, and solubility in non-polar solvents, respectively. PC scores indicating each acid's location along each of four scales were obtained. Literature data for acid flavor thresholds in beer were modeled as a function of the principal components using multiple linear regression and partial least squares (PLS) regression. The best-fit and best prediction equations were identical, with an R2 of 0·905. ©
Low-resolution 1H NMR and high-resolution 31P NMR were used to study the absorption of gadolinium (Gd) by the root tissues of maize seedlings. Gd was supplied as either Gd3+ or Gd(DTPA)2−, and its presence in the tissue caused changes in the relaxation properties of the tissue water and of various phosphorylated metabolites. 1H NMR relaxation measurements indicated that soluble Gd accumulated in the tissue more rapidly with Gd(DTPA)2− than with Gd3+, and this was attributed to the precipitation of Gd3+ in the root. Electron microscopy and x-ray microanalysis confirmed the presence of deposits containing Gd and phosphorus (P) in the extracellular space of the tissue. 31P NMR showed the presence of soluble Gd in both the cytoplasm and the vacuole of roots treated with Gd3+ and, thus, proved that Gd3+ can reach the symplast, contrary to the usual assumption about the lanthanides. Evidence for the immobilization of P by Gd3+ and for the vacuolar breakdown of Gd(DTPA)2− was also obtained from the 31P NMR spectra.
Significance:
The imino acid proline is utilized by different organisms to offset cellular imbalances caused by environmental stress. The wide use in nature of proline as a stress adaptor molecule indicates that proline has a fundamental biological role in stress response. Understanding the mechanisms by which proline enhances abiotic/biotic stress response will facilitate agricultural crop research and improve human health.
Recent advances:
It is now recognized that proline metabolism propels cellular signaling processes that promote cellular apoptosis or survival. Studies have shown that proline metabolism influences signaling pathways by increasing reactive oxygen species (ROS) formation in the mitochondria via the electron transport chain. Enhanced ROS production due to proline metabolism has been implicated in the hypersensitive response in plants, lifespan extension in worms, and apoptosis, tumor suppression, and cell survival in animals.
Critical issues:
The ability of proline to influence disparate cellular outcomes may be governed by ROS levels generated in the mitochondria. Defining the threshold at which proline metabolic enzyme expression switches from inducing survival pathways to cellular apoptosis would provide molecular insights into cellular redox regulation by proline. Are ROS the only mediators of proline metabolic signaling or are other factors involved?
Future directions:
New evidence suggests that proline biosynthesis enzymes interact with redox proteins such as thioredoxin. An important future pursuit will be to identify other interacting partners of proline metabolic enzymes to uncover novel regulatory and signaling networks of cellular stress response.
Aims
The aim of this work was to investigate the effects of rare earth elements lanthanum (La3+) and gadolinium (Gd3+) on root system architecture and interactions with low phosphate signaling in Arabidopsis thaliana.
Methods
Detailed analysis of root system architecture was performed in Arabidopsis WT seedlings and in low phosphorus insensitive mutants lpi1-3 and lpr1-1 lpr2-1 in response to REEs. Expression studies of P-deficiency regulated phosphate transporters AtPT1, AtPT2 and AtMGD2 were also conducted. The role of auxin as a mediator of root morphogenetic changes by Gd3+ was evaluated by using the auxin-inducible marker gene DR5:uidA and auxin-signaling mutants tir1, tir1 afb2 afb3, arf7, arf19 and arf7 arf19.
Results
We found that increasing concentrations of REEs inhibited primary root growth and increased root hair and lateral root development in WT seedlings. These effects were reduced in low phosphorus insensitive mutants lpi1-3 and lpr1-1 lpr2-1. Gd3+ activated the expression of AtPT1, AtPT2 and AtMGD2 markers. Lateral root formation by Gd3+ decreased in tir1 afb2 afb3 and arf7 arf19 mutants.
Conclusions
Our results suggest that REEs affect RSA in Arabidopsis by inducing low-P adaptive responses by creating P deficiency conditions in the growth medium by precipitating phosphate.
Arbuscular mycorrhizal fungi (AMF) are beneficial for the plant growth under heavy metal stress. Such beneficial effect is improved by elevated CO2 (eCO2). However, the mechanisms by which eCO2 improves AMF symbiotic associations under arsenite (AsIII) toxicity are hardly studied. Herein, we compared these regulatory mechanisms in species from two agronomical important plant families – grasses (wheat) and legumes (soybean). AsIII decreased plant growth (i.e., 53.75 and 60.29% of wheat and soybean, respectively) and photosynthesis. It also increased photorespiration and oxidative injury in both species, but soybean was more sensitive to oxidative stress as indicated by higher H2O2 accumulation and oxidation of protein and lipid. eCO2 significantly improved AMF colonization by increasing auxin levels, which induced high carotenoid cleavage dioxygenase (CCDs) activity, particularly in soybean roots. The improved sugar metabolism in plant shoots by co-application of eCO2 and AsIII allocated more sugars to roots sequentially. Sugar accumulation in plant roots is further induced by AMF, resulting in more C skeletons to produce organic acids, which are effectively exudated into the soil to reduce AsIII uptake. Exposure to eCO2 reduced oxidative damage and this mitigation was stronger in soybean. This could be attributed to a greater reduction in photorespiration as well as a stronger antioxidant and detoxification defence systems. The grass/legume-specificity was supported by principal component analysis, which revealed that soybean was more affected by AsIII stress and more responsive to AMF and eCO2. This study provided a mechanistic understanding of the impact of AMF, eCO2 and their interaction on As-stressed grass and legume plants, allowing better practical strategies to mitigate AsIII phytotoxicity.
Nano-sized arsenic oxide nanoparticles (As2O3-NP) limit crop growth and productivity. As2O3-NP represent a strong environmental hazard. The predicted rise in future atmospheric CO2 could boost plant growth both under optimal and heavy metal stress conditions. So far, the phytotoxicity of As2O3-NP and their interaction with eCO2 were not investigated at physiological and metabolic levels in crop species groups such as C3 and C4. We investigated how eCO2 level (620 ppm) alleviated soil As2O3-NP toxicity induced growth and mitigated oxidative damages through analysing photosynthetic parameters, primary (sugars and amino acids) and secondary (phenolics, flavonoids and anthocyanins) metabolism in C3 (barley) and C4 (maize) plants. Compared to maize, barley accumulated higher As2O3-NP level, which inhibited growth and induced oxidative damage particularly in barley (increased H2O2 and lipid peroxidation). Interestingly, eCO2 differently mitigated As2O3-NP toxicity on photosynthesis, which consequently improved sugar metabolism. Moreover, high carbon availability in eCO2 treated plants directed to produce osmo-protectant (soluble sugars and proline) and antioxidants (anthocyanins and tocopherols). In the line with increased proline and anthocyanins, their metabolism was also improved. Notable differences occurred between the two plant species. The ornithine pathway was preferred in maize while in barley proline accumulation was mainly through glutamate pathway. Moreover, under As2O3-NP stress, barley preferentially accumulated anthocyanins while maize accumulated total phenolics and flavonoids. This work contributes to improving our understanding of the differences in growth, physiological and biochemical responses of major crops of two functional photosynthetic groups (C3 and C4 plants) under ambient and elevated CO2 grown under As2O3-NP stress.
Rare Earth Elements (REEs) are increasingly being used in agriculture and are also used to produce high end technological devices, thereby increasing their anthropogenic presence in the environment. However, the ecotoxicological mechanism of REEs on organisms is not fully understood. In this study, the effects of gadolinium (Gd) addition on Arabidopsis thaliana (L.) were investigated at both physiological and molecular levels. Four treatments (0, 10, 50 and 200 μmol·L⁻¹ Gd) were used in the exposure tests. Biomass, root length and chlorophyll content in shoots/roots were measured to investigate the plant’s physiological response to Gd stress. Random amplified polymorphic (RAPD)-Polymerase Chain Reaction (PCR) and methylation sensitive arbitrarily primed (MSAP)-PCR were used to investigate changes in genetic variation and DNA methylation of A. thaliana when exposed to Gd. At the physiological level, it was found that low concentration of Gd (10 μmol·L⁻¹) could significantly increase the plant biomass and root length, while the growth of A. thaliana was significantly inhibited when exposed to 200 μmol·L⁻¹ of Gd, yet the total soluble protein content in aerial plant parts increased significantly by 24.2% when compared to the control group. Among the 12 primers considered in the RAPD assessment, at the molecular level, only four primers revealed different patterns in their genomic DNA. Compared to the control group, the treatment with 50 μmol·L⁻¹ of Gd was associated with lower polymorphism, while the treatment with 200 μmol·L⁻¹ of Gd was associated with higher polymorphism. The polymorphism frequencies for the 50 μmol·L⁻¹ of Gd and the 200 μmol·L⁻¹ of Gd were 4.67% and 20.33%, respectively. The MSAP analysis revealed that the demethylation (D) type of Arabidopsis genomic DNA increased significantly under 10 and 50 μmol·L⁻¹ of Gd, while the methylation (M) type was also significantly increased under 200 μmol·L⁻¹ of Gd. Generally, the total methylation polymorphism (D+M) increased with an increase of Gd concentration. It was found that high concentrations of Gd appeared to cause DNA damage, but low concentrations of Gd (as low as 10 μmol·L⁻¹) were associated with DNA methylation change. Further, it was verified by Real time Reverse Transcription PCR (RT-PCR) on the bands detected by the MSAP analysis, that the genes relative to processes including cell cycle, oxidative stress and apoptosis, appeared to be regulated by methylation under Gd stress. These findings reveal new insight regarding ecotoxicity mechanisms of REEs on plants.
Future climate CO2 (eCO2) and contamination with nano-sized heavy metals (HM-NPs) represent concurrent challenges threatening plants. The interaction between eCO2 and HM-NPs is rarely investigated, and no study has addressed their synchronous impact on the metabolism of the multifunctional stress-related metabolites, such as sugars and amino acids. Moreover, the characteristic responses of C3 and C4 plant systems to the concurrent impact of eCO2 and HM-NPs are poorly understood. Herein, we have assessed the impact of eCO2 (620 ppm) and/or HgO-NPs (100 mg/Kg soil) on growth, physiology and metabolism of sugars and amino acids, particularly proline, in C3 (wheat) and C4 (maize) plant systems. Under Hg-free conditions, eCO2 treatment markedly improved the growth and photosynthesis and induced sugars levels and metabolism (glucose, fructose, sucrose, starch, sucrose P synthase and starch synthase) in wheat (C3) only. In contrast, HgO-NPs induced the uptake, accumulation and translocation of Hg in wheat and to less extend in maize plants. Particularly in wheat, this induced significant decreases in growth and photosynthesis and increases in photorespiration, dark respiration and levels of tricarboxylic acid cycle organic acids. Interestingly, the co-application of eCO2 reduced the accumulation of Hg and recovered the HgO-NPs-induced effects on growth and metabolism in both plants. At stress defense level, HgO-NPs induced the accumulation of sucrose and proline, more in maize, via upregulation of sucrose P synthase, ornithine amino transferase, ∆1-pyrroline-5-carboxylate (P5C) synthetase and P5C reductase. The co-existence of eCO2 favored reduced sucrose biosynthesis and induced proline catabolism, which provide high energy to resume plant growth. Overall, despite the difference in their response to eCO2 under normal conditions, eCO2 induced similar metabolic events in C3 and C4 plants under stressful conditions, which trigger stress recovery.
Alfalfa sprouts are well known for its nutritive values. Although there are several studies reported the positive impact of elevated CO2 (eCO2) on plants, there is no in-depth, comprehensive studies on how eCO2 could improve the sprouting of plant seeds. Herein, the production of health-promoting metabolites was determined in eCO2 (620 ppm) treated Alfalfa sprout cultivars (Giza 1, Nubaria and Ismailia 1). eCO2 increased the photosynthetic process and pigment contents, which consequently induced carbohydrates, proteins, fats and fibers accumulation. eCO2 also boosted the levels of vitamins, phenolics, flavonoids and mineral individuals and enhanced the antioxidant capacity of alfalfa sprouts. Interestingly, eCO2 reduced the antinutritional factor L-canavanine content in Ismailia 1 cultivar and improved the anti-inflammatory activities through inhibiting cyclooxygenase-2 and lipoxygenase activity. Therefore, eCO2 is a promising approach to improve the health-promoting prospective of alfalfa sprouts to be a valuable source of nutritious and bioactive compounds in our daily diet.
Rising atmospheric [CO2] influences plant growth, development, productivity and stress responses. Soybean is a major oil crop. At present, it is unclear how elevated [CO2] affects the physiological and biochemical pathways of soybean under drought stress. In this study, changes in the photosynthetic capacity, photosynthetic pigment and antioxidant level were evaluated in soybean at flowering stages under different [CO2] (400 μmol mol⁻¹ and 600 μmol mol⁻¹) and water level (the relative water content of the soil was 75–85% soil capacity, and the relative water content of the soil was 35–45% soil capacity under drought stress). Changes in levels of osmolytes, hormones and signal transduction enzymes were also determined. The results showed that under drought stress, increasing [CO2] significantly reduced leaf transpiration rate (E), net photosynthetic rate (PN) and chlorophyll b content. Elevated [CO2] significantly decreased the content of malondialdehyde (MDA) and proline (PRO), while significantly increased superoxide dismutase (SOD) and abscisic acid (ABA) under drought stress. Elevated [CO2] significantly increased the transcript and protein levels of calcium-dependent protein kinase (CDPK). And Glutathione S- transferase (GST). The content of HSP-70 and the corresponding gene expression level were significantly reduced by elevated [CO2], irrespective of water treatments. Taken together, these results suggest that elevated [CO2] does not alleviate the negative impacts of drought stress on photosynthesis. ABA, CDPK and GST may play an important role in elevated CO2-induced drought stress responses.
This book presents the state-of-the-art in plant ecophysiology. With a particular focus on adaptation to a changing environment, it discusses ecophysiology and adaptive mechanisms of plants under climate change. Over the centuries, the incidence of various abiotic stresses such as salinity, drought, extreme temperatures, atmospheric pollution, metal toxicity due to climate change have regularly affected plants and, and some estimates suggest that environmental stresses may reduce the crop yield by up to 70%. This in turn adversely affects the food security. As sessile organisms, plants are frequently exposed to various environmental adversities. As such, both plant physiology and plant ecophysiology begin with the study of responses to the environment. Provides essential insights, this book can be used for courses such as Plant Physiology, Environmental Science, Crop Production and Agricultural Botany.
Volume 2 provides up-to-date information on the impact of climate change on plants, the general consequences and plant responses to various environmental stresses.
Abiotic stresses are major threats influencing crop growth and production globally. Abiotic stresses can cause several cellular dysfunctions, and some of them are beneficial and required for stress tolerance enhancement. Compatible solute accumulation is one of these changes, and among them proline (Pro) overproduction is a physiological response commonly found in plants exposed to various abiotic stresses. Pro overproduction has been proposed to correlate with stress resistance in many plants. Pro implication in stress tolerance mechanism is supported by the observations that exogenous supply and genetic manipulation of metabolic pathways associated with Pro biosynthesis have been beneficial in enhancing stress tolerance in many plant species under different stresses. Pro improves stress tolerance via acting as a stress-related signal influencing adaptive responses, osmotic adjustment mediator, and molecular chaperone to stabilize subcellular structures, scavenging reactive oxygen species (ROS), acting as a metal chelator, serving as a nitrogen/carbon source for cells under stress conditions and after stress relief, maintaining cytoplasmic pH and hence alleviating its acidosis, triggering gene expression, and buffering cellular redox potential. Pro actual role in conferring stress tolerance is, however, still a matter of debate because there are several inconsistencies among published data. Also, Pro biosynthesis is dependent on a high diversity of regulation mechanisms, and even several of them are still largely obscure, which might exacerbate these discrepancies. Furthermore, the broad natural variation in Pro overproduction and its true role in metabolism of plants under stress conditions necessitate further research for better understanding of the reported variations. Despite the Pro beneficial roles observed under stress conditions, we believe that the often proposed relationship between Pro production and stress resistance may not be universal.
Elevated atmospheric CO2 concentration (e[CO2]) and soil
water deficits have substantial effect on stomatal morphology
and movement that regulate plant water relations and plant
growth. e[CO2] could alleviate the impact of drought stress,
thus contributing to crop yield. Xylem-borne abscisic acid
(ABA) plays a crucial role in regulating stomatal aperture
serving as first line of defence against drought; whereas e[CO2]
may disrupt this fundamental drought adaptation mechanism
by delaying the stomatal response to soil drying. We review the
state-of-the-art knowledge on stomatal response to drought
stress at e[CO2] and discuss the role of ABA in mediating these
responses.
Due to industrialization and expansion of nanotechnology, ecosystem contamination by nanoparticles is likely. Overall, nanoparticles accumulate in environmental matrices and induce phytotoxicity, however future climate (elevated CO2 (eCO2)) may affect the distribution of nanoparticles in ecosystems and alter their impact on plants. In the current study, nickel oxide nanoparticles (NiO-NPs) with an average diameter of 54 nm were synthesized using Triton X-100 and characterized by scanning electron microscopy (SEM), UV-VIS spectroscopy and Fourier transform infrared spectroscopy (FTIR). We have investigated the impact of NiO-NPs at a concentration of 120 mg kg−1 soil, selected based on the results of a preliminary experiment, on accumulation of Ni ions in wheat (Triticum aestivum L.) and how that could influence plant growth, photosynthesis and redox homeostasis under two CO2 scenarios, ambient (aCO2, 400 ppm) and eCO2 (620 ppm). NiO-NPs alone reduced whole plant growth, inhibited photosynthesis and increased the levels of antioxidants. However, improved defense system was not enough to lessen photorespiration induced H2O2 accumulation and oxidative damage (lipid and protein oxidation). Interestingly, eCO2 significantly mitigated the phytotoxicity of NiO-NPs. Although, eCO2 did not affect Ni accumulation and translocation in wheat, it promoted photosynthesis and inhibited photorespiration, resulting in reduced ROS production. Moreover, it further improved the antioxidant defense system and maintained ASC/DHA and GSH/GSSG redox balances. Organ specific responses to NiO-NPs and/or eCO2 were indicated and confirmed by cluster analysis. Overall, we suggest that wheat plants will be more tolerant to NiO-NPs stress under future climate CO2.
Many studies have discussed the influence of elevated carbon dioxide (eCO2) on modeling and crop plants. However, much less effort has been dedicated to herbal plants. In this study, a robust monitoring for the levels of 94 primary and secondary metabolites and minerals in two medicinal herbs, basil (Ocimum basilicum L.) and peppermint (Mentha piperita L.), grwon under both ambient (aCO2, 360 ppm) and eCO2 (620 ppm) was performed. We also assessed how the changes in herbal tissue chemistry affected their biological activity. Elevated CO2 significantly increased herbal biomass, improved the rates of photosynthesis and dark respiration, and altered the tissue chemistry. Principal Component Analysis of the full data set revealed that eCO2 induced a global change in the metabolomes of the two plants. Moreover, Hierarchical Clustering Analyses showed quantitative differences in the metabolic profiles of the two plants and in their responsiveness to eCO2. Out of 94 metabolites, 38 and 31 significantly increased in basil and peppermint, respectively, as affected by eCO2. Regardless of the plant species, the levels of non-structural carbohydrates, fumarate, glutamine, glutathione, ascorbate, phylloquinone (vitamin K1), anthocyanins and a majority of flavonoids and minerals were significantly improved by eCO2. However, some metabolites tended to show species specificity. Interestingly, eCO2 caused enhancement in antioxidant, antiprotozoal, anti-bacterial and anticancer (against urinary bladder carcinoma; T24P) activities in both plants, which was consequent with improvement in the levels of antioxidant metabolites such as glutathione, ascorbate and flavonoids. Therefore, this study suggests that the metabolic changes triggered by eCO2 in the target herbal plants improved their biological activities.
Soybean (Glycine max L.) is often cultivated in areas contaminated with arsenic (As), which negatively affects plant growth and reduces crop yield. The deleterious effects may be due, at least in part, to disturbances in the water status, as was reported for some plants exposed to heavy metals. However, to our knowledge, these mechanisms have not been studied in depth in soybean plants exposed to As. The aim of the present work was to analyze possible changes in water relations and the responses developed in soybean plants under arsenate (AsV) and arsenite (AsIII) stress. We discuss physiological and morphological aspects of the As stress response, such as root absorption rate, water content, stomatal conductance, water and osmotic potential, accumulation of compatible solutes, leaf conducting tissues and stomata characteristics. AsV and AsIII caused a significant decrease in root absorption rate, which could reduce metalloid uptake. On the other hand, water content decreased at the beginning of the treatment but was re-established after 4 and 8 d. This was correlated with a decrease in stomatal conductance and a reduction in leaf water and osmotic potential due to the accumulation of proline and soluble sugars. Besides, smaller leaf xylem vessels and abnormal stomata were observed in plants under As treatment. These mechanisms increased the plant's ability to retain water and therefore to avoid dehydration. Thus, the results of the present work contribute to the understanding of how soybean responds to As, by describing key tolerance strategies to the metalloid.
Soil contamination by heavy metals in combination with elevated atmospheric CO2 has important effects on the rhizosphere microenvironment by influencing plant growth. Here, we investigated the response of the R. pseudoacacia rhizosphere microenvironment to elevated CO2 in combination with cadmium (Cd)- and lead (Pb)-contamination. Organic compounds (total soluble sugars, soluble phenolic acids, free amino acids, and organic acids), microbial abundance and activity, and enzyme activity (urease, dehydrogenase, invertase, and β-glucosidase) in rhizosphere soils increased significantly (p < 0.05) under elevated CO2 relative to ambient CO2; however, l-asparaginase activity decreased. Addionally, elevated CO2 alone affected soil microbial community in the rhizosphere. Heavy metals alone resulted in an increase in total soluble sugars, free amino acids, and organic acids, a decrease in phenolic acids, microbial populations and biomass, and enzyme activity, and a change in microbial community in rhizosphere soils. Elevated CO2 led to an increase in organic compounds, microbial populations, biomass, and activity, and enzyme activity (except for l-asparaginase), and changes in microbial community under Cd, Pb, or Cd + Pb treatments relative to ambient CO2. In addition, elevated CO2 significantly (p < 0.05) enhanced the removal ratio of Cd and Pb in rhizosphere soils. Overall, elevated CO2 benefited the rhizosphere microenvironment of R. pseudoacacia seedlings under heavy metal stress, which suggests that increased atmospheric CO2 concentrations could have positive effects on soil fertility and rhizosphere microenvironment under heavy metals.
Flavonoids, with various biological activities, are considered as key compounds in propolis. In this study, quantitative determinations of flavonoids in propolis were conducted by two complementary colorimetric methods, aluminum chloride method and 2,4-dinitrophenylhydrazine method. Results suggested that the sum of flavonoid contents determined by the above two individual methods may represent the real content of total flavonoids. In this work, six raw propolis samples were investigated and the total contents of flavonoids ranged from 10.38 ± 0.14% to 24.91 ± 0.53%. As for the 12 commercial propolis products examined, the levels of total flavonoids in tinctures were all below 7% and those in powdery products varied from 2.97 ± 0.05% to 22.73 ± 0.72%.
Physiology, oxidative stress and production of metabolites in Hypericum perforatum exposed to moderate Cd and/or La concentration (10μM) were studied. La evoked increase in reactive oxygen species, malondialdehyde and proline but suppressed growth, tissue water content, glutathione, ascorbic acid and affected mineral nutrient contents more than Cd while the impact of Cd+La was not synergistic. Similar trend was observed at the level of superoxide dismutase gene expression. Shoot Cd amount increased in Cd+La while only root La increased in the same treatment. Extensive quantification of secondary metabolites revealed that La affected phenolic acids more pronouncedly than Cd in shoots and roots. Flavonols were suppressed by La that could contribute to the appearance of oxidative damage. Procyanidins increased in response to La in the shoots but decreased in the roots. Metabolic responses in Cd+La treatment resembled those of La treatment (almost identically in the roots). Phenylalanine ammonia-lyase activity was mainly suppressed by La. The presence of La also depleted amount of hypericin and expression of its putative gene (hyp-1) showed similar trend but accumulation of hyperforin increased under Cd or La excess. Clear differences in the stem and root anatomy in response to Cd or La were also found. Overall, H. perforatum is La-sensitive species and rather Cd ameliorated negative impact of La.
Copyright © 2014 Elsevier B.V. All rights reserved.
Since their early migration from aquatic environments to the land, plants have had to cope with periodic and unpredictable environmental stresses during growth and development. Surviving such stresses over a long evolutionary scale led plants to acquire mechanisms by which they can sensitively perceive incoming stresses and regulate their physiology accordingly. The plant hormone abscisic acid (ABA) plays a major role in plant responses to stress. Although rapid production of ABA in response to drought and salt stresses is essential to define ABA as a stress hormone, an equally rapid catabolism of ABA when such stresses are relieved is also essential in that role. Since ABA mediates so many stress responses, the initial perception of dehydration and the subsequent changes in gene expression that lead to rapid ABA biosynthesis constitute the most important stress signal transduction pathway among all the plant responses to stresses. Identification of the genes involved and understanding their roles during stress perception and physiological regulation has become an important and exciting research field in recent years. This review covers mainly our understanding of this aspect. ABA-induced changes in gene expression and their roles in physiological regulation are dealt with in less detail.
Many teleosts have evolved mechanisms to cope with ammonia toxicity in the brain when confronted
with high environmental ammonia (HEA). In the present study, the possible role of conversion of accumulated ammonia to glutamine and other free amino acids in the brain of three freshwater teleosts
differing in their sensitivities to ammonia was investigated. The detoxification mode of ammonia in
brain is suggested to be through amination of glutamate to glutamine by the coupled activities of
glutamate dehydrogenase (GDH), transaminase (aspartate aminotransaminase ‘AST’ and alanine aminotransaminase ‘ALT’) and glutamine synthetase (GSase). We investigated the metabolic response of amino acids in the brain of highly sensitive salmonid Oncorhynchus mykiss (rainbow trout), the less sensitive cyprinid Cyprinus carpio (common carp) and the highly resistant cyprinid Carassius auratus (goldfish) when exposed to 1 mM ammonia (as NH4HCO3; pH 7.9) for 0 h (control), 3 h, 12 h, 24 h, 48 h, 84 h and 180 h. Results show that HEA exposure increased ammonia accumulation significantly in the brain of all the three species from 12 h onwards. Unlike in trout, ammonia accumulation in carp and goldfish was
restored to control levels (48–84 h); which was accompanied with a significant increase in glutamine
content as well as GSase activity. In trout, glutamine levels also increased (84–180 h) but GSase was
not activated. The elevated glutamine level in trout was accompanied by a significant depletion of the
glutamate pool in contrast to the stable glutamate levels seen in carp and goldfish. This suggests a simultaneous increase in the rate of glutamate formation to match with the demand of glutamine formation
in cyprinids. The activity of GDH was elevated significantly in carp and goldfish but remained unaltered
in trout. Also, the transaminase enzymes (AST and ALT) were elevated significantly in exposed carp and
goldfish while only ALT was up-regulated in trout. Consequently, in carp and goldfish both aspartate and
alanine were utilized under HEA, whereas only alanine was consumed in trout. With ammonia treatment,
significant changes in concentrations of other amino acids also occurred. None of the species could
detoxify brain ammonia into urea. This study suggests that protective strategies to combat ammonia
toxicity in brain are more pronounced in carp and goldfish than in trout.