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Integrated metabolomics and transcriptomics analysis reveals γ-aminobutyric acid enhances the ozone tolerance of wheat by accumulation of flavonoids
... After UV-B radiation, most of the flavonoid contents of R. chrysanthum increased, with flavone, flavonol, and flavanone contents increasing in the majority of species ( Figure 4D). Similar accumulations of dihydroflavonoids, flavonols, and flavanols were found in wheat after ozone stress in previous reports [53]. These classes of flavonoids have been reported to function in plant vesicles or chloroplasts for effective scavenging of hydrogen peroxide (H 2 O 2 ) and monoclinic oxygen to mitigate the damage caused by stress conditions on their own [54]. ...
With the depletion of the ozone layer, the intensity of ultraviolet B (UV-B) radiation reaching the Earth’s surface increases, which in turn causes significant stress to plants and affects all aspects of plant growth and development. The aim of this study was to investigate the mechanism of response to UV-B radiation in the endemic species of Rhododendron chrysanthum Pall. (R. chrysanthum) in the Changbai Mountains and to study how exogenous ABA regulates the response of R. chrysanthum to UV-B stress. The results of chlorophyll fluorescence images and OJIP kinetic curves showed that UV-B radiation damaged the PSII photosystem of R. chrysanthum, and exogenous ABA could alleviate this damage to some extent. A total of 2148 metabolites were detected by metabolomics, of which flavonoids accounted for the highest number (487, or 22.67%). KEGG enrichment analysis of flavonoids that showed differential accumulation by UV-B radiation and exogenous ABA revealed that flavonoid biosynthesis and flavone and flavonol biosynthesis were significantly altered. GO analysis showed that most of the DEGs produced after UV-B radiation and exogenous ABA were distributed in the cellular process, cellular anatomical entity, and catalytic activity. Network analysis of key DFs and DEGs associated with flavonoid synthesis identified key flavonoids (isorhamnetin-3-O-gallate and dihydromyricetin) and genes (TRINITY_DN2213_c0_g1_i4-A1) that promote the resistance of R. chrysanthum to UV-B stress. In addition, multiple transcription factor families were found to be involved in the regulation of the flavonoid synthesis pathway under UV-B stress. Overall, R. chrysanthum actively responded to UV-B stress by regulating changes in flavonoids, especially flavones and flavonols, while exogenous ABA further enhanced its resistance to UV-B stress. The experimental results not only provide a new perspective for understanding the molecular mechanism of the response to UV-B stress in the R. chrysanthum, but also provide a valuable theoretical basis for future research and application in improving plant adversity tolerance.
Elevated concentrations of tropospheric ozone (O3) pose a significant threat to food production in many regions of the world. We conducted a two-year experiment with five winter wheat (Triticum aestivum L.) cultivars, Yangmai16 (Y16), Yangmai23 (Y23), Zhenmai12 (Z12), Yangmai29 (Y29), and Yangmai30 (Y30), to assess photosynthetic traits, lipid peroxidation, and antioxidant systems under ambient (A-O3) or elevated (E-O3; 1.5 times A-O3) O3 in a Free-Air O3-Concentration Enrichment system (FACE). E-O3 accelerated leaf senescence, manifested by marked reductions in photosynthetic rate, stomatal conductance, total antioxidant capacity, and photosynthetic pigment content, accompanied by altered antioxidant enzyme activity and a significant increase in malondialdehyde content (an indicator of lipid peroxidation). Most parameters showed significant inter-cultivar differences, as well as interactions between O3 and cultivar. The response of the antioxidant system in wheat flag leaves was influenced by O3 exposure levels. The response of antioxidant enzymes at the grain filling stage and the timely closure of stomata conferred tolerance to O3. This tolerance was associated with higher antioxidant enzyme activity at the anthesis stage but was not related to the size of stomata. This study provides a crucial theoretical foundation for further breeding O3-tolerant cultivars.
The deleterious effects of ozone (O 3 ) pollution on crop physiology, yield, and productivity are widely acknowledged. It has also been assumed that C 4 crops with a carbon concentrating mechanism and greater water use efficiency are less sensitive to O 3 pollution than C 3 crops. This assumption has not been widely tested. Therefore, we compiled 46 journal articles and unpublished datasets that reported leaf photosynthetic and biochemical traits, plant biomass, and yield in five C 3 crops (chickpea, rice, snap bean, soybean, and wheat) and four C 4 crops (sorghum, maize, Miscanthus × giganteus , and switchgrass) grown under ambient and elevated O 3 concentration ([O 3 ]) in the field at free-air O 3 concentration enrichment (O 3 -FACE) facilities over the past 20 y. When normalized by O 3 exposure, C 3 and C 4 crops showed a similar response of leaf photosynthesis, but the reduction in chlorophyll content, fluorescence, and yield was greater in C 3 crops compared with C 4 crops. Additionally, inbred and hybrid lines of rice and maize showed different sensitivities to O 3 exposure. This study quantitatively demonstrates that C 4 crops respond less to elevated [O 3 ] than C 3 crops. This understanding could help maintain cropland productivity in an increasingly polluted atmosphere.
Tropospheric ozone (O3) is a secondary pollutant that causes oxidative stress in plants due to the generation of excess reactive oxygen species (ROS). Phenylpropanoid metabolism is induced as a usual response to stress in plants, and induction of key enzyme activities and accumulation of secondary metabolites occur, upon O3 exposure to provide resistance or tolerance. The phenylpropanoid, isoprenoid, and alkaloid pathways are the major secondary metabolic pathways from which plant defense metabolites emerge. Chronic exposure to O3 significantly accelerates the direction of carbon flows toward secondary metabolic pathways, resulting in a resource shift in favor of the synthesis of secondary products. Furthermore, since different cellular compartments have different levels of ROS sensitivity and metabolite sets, intracellular compartmentation of secondary antioxidative metabolites may play a role in O3-induced ROS detoxification. Plants’ responses to resource partitioning often result in a trade-off between growth and defense under O3 stress. These metabolic adjustments help the plants to cope with the stress as well as for achieving new homeostasis. In this review, we discuss secondary metabolic pathways in response to O3 in plant species including crops, trees, and medicinal plants; and how the presence of this stressor affects their role as ROS scavengers and structural defense. Furthermore, we discussed how O3 affects key physiological traits in plants, foliar chemistry, and volatile emission, which affects plant–plant competition (allelopathy), and plant–insect interactions, along with an emphasis on soil dynamics, which affect the composition of soil communities via changing root exudation, litter decomposition, and other related processes.
Powdery mildew is a fungal disease devastating to wheat, causing significant quality and yield loss. Flavonoids are important secondary plant metabolites that confer resistance to biotic and abiotic stress. However, whether they play a role in powdery mildew resistance in wheat has yet to be explored. In the present study, we combined transcriptome and metabolome analyses to compare differentially expressed genes (DEGs) and differentially accumulated flavonoids identified in plants with and without powdery mildew inoculation. Transcriptome analysis identified 4,329 DEGs in susceptible wheat cv. Jimai229, and 8,493 in resistant cv. HHG46. The DEGs were functionally enriched using Gene Ontology and Kyoto Encyclopedia of Genes and Genomes, revealing the flavonoid synthesis pathway as the most significant in both cultivars. This was consistent with the upregulation of flavonoid synthesis pathway genes observed by quantitative PCR. Metabolome analysis indicated flavone and flavonol biosynthesis pathways as the most significantly enriched following powdery mildew inoculation. An accumulation of total flavonoids content was also found to be induced by powdery mildew infection. Exogenous flavonoids treatment of inoculated plants led to less severe infection, with fewer and smaller powdery mildew spots on the wheat leaves. This reduction is speculated to be regulated through malondialdehyde content and the activities of peroxidase and catalase. Our study provides a fundamental theory for further exploration of the potential of flavonoids as biological prevention and control agents against powdery mildew in wheat.
Surface ozone is a damaging pollutant for crops and ecosystems, and the ozone-induced crop losses over India remain uncertain and a topic of debate due to a lack of sufficient observations and uncertainties involved in the modeled results. In this study, we have used the observational data from MAPAN (Modelling Air Pollution And Networking) for the first time to estimate the relative yield losses, crop production losses, and economic losses for the two major crops (wheat and rice). The detailed estimation has been done focusing on three individual suburban sites over India (Patiala, Tezpur, and Delhi) and compared with other related studies over the Indian region. We have used the concentration-based metric (M7, 7-h average from 09:00 to 15:59 h) along with the cumulative ozone exposure indices (AOT40, accumulated exposure over a threshold of 40 ppb) and applied the exposure–response (E-R) functions for the calculation of the crop losses. Our study shows that the yearly crop losses can reach the level of 12.4–40.8% and 2.0–11.1% for the wheat and rice crops, respectively, at certain places like Patiala in India. The annual economic loss can be as high as $4.6 million and $0.7 million for wheat and rice crops, respectively, even at individual locations in India. Our estimated %RYL (relative yield loss) lies in the range of 0.3 + /0.6 times the recent regional model estimates which use only the AOT40 metric. Region-specific E-R functions based on factors suitable for the Indian region needs to be developed.
East Asia is a hotspot of surface ozone (O3) pollution, which hinders crop growth and reduces yields. Here, we assess the relative yield loss in rice, wheat and maize due to O3 by combining O3 elevation experiments across Asia and air monitoring at about 3,000 locations in China, Japan and Korea. China shows the highest relative yield loss at 33%, 23% and 9% for wheat, rice and maize, respectively. The relative yield loss is much greater in hybrid than inbred rice, being close to that for wheat. Total O3-induced annual loss of crop production is estimated at US$63 billion. The large impact of O3 on crop production urges us to take mitigation action for O3 emission control and adaptive agronomic measures against the rising surface O3 levels across East Asia.
Article Ca 2+ sensor-mediated ROS scavenging suppresses rice immunity and is exploited by a fungal effector Graphical abstract Highlights d Rice ROD1 suppresses immunity via catalase activation and ROS scavenging d ROD1 is a Ca 2+-sensor fine-tuned by ubiquitination-mediated protein degradation d Natural ROD1 variants influence indica and japonica rice immunity d The fungal effector AvrPiz-t exploits the ROD1 cascade to promote virulence In brief ROD1 encodes a Ca 2+ sensor to suppress rice immunity by promoting ROS scavenging. The fungal effector AvrPiz-t structurally mimics ROD1 and shares the same ROS-elimination cascade to suppress rice immunity and promote virulence. SUMMARY Plant immunity is activated upon pathogen perception and often affects growth and yield when it is consti-tutively active. How plants fine-tune immune homeostasis in their natural habitats remains elusive. Here, we discover a conserved immune suppression network in cereals that orchestrates immune homeostasis, centering on a Ca 2+-sensor, RESISTANCE OF RICE TO DISEASES1 (ROD1). ROD1 promotes reactive oxygen species (ROS) scavenging by stimulating catalase activity, and its protein stability is regulated by ubiquitina-tion. ROD1 disruption confers resistance to multiple pathogens, whereas a natural ROD1 allele prevalent in indica rice with agroecology-specific distribution enhances resistance without yield penalty. The fungal effector AvrPiz-t structurally mimics ROD1 and activates the same ROS-scavenging cascade to suppress host immunity and promote virulence. We thus reveal a molecular framework adopted by both host and pathogen that integrates Ca 2+ sensing and ROS homeostasis to suppress plant immunity, suggesting a principle for breeding disease-resistant, high-yield crops.
Ozone concentrations near the land surface are rising in Asia while they are declining or stagnating in Europe and North America. Ozone is the most widespread air pollutant negatively affecting vegetation, and its increased concentrations pose a major threat to food quality and production and other ecosystem services in Asia. In this review, we provide an overview of scientific challenges in the impacts of ozone pollution on Asian vegetation, and synthesize the challenges toward mitigation of the impacts. We argue that new policy initiatives need to seek both reduction of ozone levels and enhancement of plant tolerance to ozone to maintain food quality and ensure food supplies. The scientific advancements must be transferred to actions by two types of institutions: a) environmental agencies for reducing ozone levels and b) agricultural research institutions for enhancing plant tolerance to ozone. In connecting the scientific advancements with the institutional actions, scientists in Asian countries should play the key role taking advantages of interdisciplinary and international collaborations.
The non-protein amino acid γ-aminobutyric acid (GABA) has been proposed to be an ancient messenger for cellular communication conserved across biological kingdoms. GABA has well-defined signalling roles in animals; however, whilst GABA accumulates in plants under stress it has not been determined if, how, where and when GABA acts as an endogenous plant signalling molecule. Here, we establish endogenous GABA as a bona fide plant signal, acting via a mechanism not found in animals. Using Arabidopsis thaliana, we show guard cell GABA production is necessary and sufficient to reduce stomatal opening and transpirational water loss, which improves water use efficiency and drought tolerance, via negative regulation of a stomatal guard cell tonoplast-localised anion transporter. We find GABA modulation of stomata occurs in multiple plants, including dicot and monocot crops. This study highlights a role for GABA metabolism in fine tuning physiology and opens alternative avenues for improving plant stress resilience. GABA accumulates during stress in plants but how, where and when GABA acts is not clear. Here the authors show that GABA production in Arabidopsis guard cells reduces stomatal opening and transpirational water loss, thereby improving water use efficiency.
Surface ozone (O3) pollution poses significant threats to crop production and food security worldwide, but an assessment of present-day and future crop yield losses due to exposure to O3 still abides with great uncertainties, mostly due: (1) to the large spatiotemporal variability and uncertain future projections of O3 concentration itself; (2) different methodological approaches to quantify O3 exposure and impacts; (3) difficulty in accounting for co-varying factors such as CO2 concentration and climatic conditions. In this paper, we explore these issues using a common framework: a consistent set of simulated present-day O3 fields from one chemical transport model, coupled with a terrestrial ecosystem-crop model to derive various O3 exposure metrics and impacts on relative crop yields worldwide, and examine the potential effects of elevated CO2 on O3-induced crop yield losses. Throughout, we review and explain the differences in formulation and parameterization in the various approaches, including the concentration-based metrics, flux-based metrics, and mechanistic biophysical crop modeling. We find that while the spatial pattern of yield losses for a given crop is generally consistent across metrics, the magnitudes can differ substantially. Pooling the concentration-based and flux-based metrics together, we estimate the present-day globally aggregated yield losses to be: 3.6 ± 1.1% for maize, 2.6 ± 0.8% for rice, 6.7 ± 4.1% for soybean, and 7.2 ± 7.3% for wheat; these estimates are generally consistent with previous studies but on the lower end of the uncertainty range covered. We attribute the large combined uncertainty mostly to the differences among methodological approaches, and secondarily to differences in O3 and meteorological inputs. Based on a biophysical crop model that mechanistically simulates photosynthetic and yield responses of crops to stomatal O3 uptake, we further estimate that increasing CO2 concentration from 390 to 600 ppm reduces the globally aggregated O3-induced yield loss by 21-52% for maize and by 27-38% for soybean, reflecting a CO2-induced reduction in stomatal conductance that in turn alleviates stomatal O3. Rising CO2 may therefore render the currently used exposure-yield relationships less applicable in a future atmosphere, and we suggest approaches to address such issues.
Background:
Salt stress is a serious abiotic stress that caused crop growth inhibition and yield decline. Previous studies have reported on the the synthesis of gamma-aminobutyric acid (GABA) and its relationship with plant resistance under various abiotic stress. However, the relationship between exogenous GABA alleviating plant salt stress damage and ion flux, amino acid synthesis, and key enzyme expression remains largely unclear. We investigated plant growth, Na+ transportation and accumulation, reactive oxygen species (ROS) metabolism and evaluated the effect of GABA on amino acids, especially SlGADs gene expression and the endogenous GABA content of tomato (Solanum lycopersicum L.) seedlings treated with or without 5 mmol·L- 1 GABA under 175 mmol·L- 1 NaCl stress.
Results:
Exogenous application of GABA significantly reduced the salt damage index and increased plant height, chlorophyll content and the dry and fresh weights of tomato plants exposed to NaCl stress. GABA significantly reduced Na+ accumulation in leaves and roots by preventing Na+ influx in roots and transportation to leaves. The transcriptional expression of SlGAD1-3 genes were induced by NaCl stress especially with GABA application. Among them, SlGAD1 expression was the most sensitive and contributed the most to the increase in glutamate decarboxylase (GAD) activity induced by NaCl and GABA application; Exogenous GABA increased GAD activity and amino acid contents in tomato leaves compared with the levels under NaCl stress alone, especially the levels of endogenous GABA, proline, glutamate and eight other amino acids. These results indicated that SlGADs transcriptional expression played an important role in tomato plant resistance to NaCl stress with GABA application by enhancing GAD activity and amino acid contents. GABA significantly alleviated the active oxygen-related injury of leaves under NaCl stress by increasing the activities of antioxidant enzymes and decreasing the contents of active oxygen species and malondialdehyde.
Conclusion:
Exogenous GABA had a positive effect on the resistance of tomato seedlings to salt stress, which was closely associated with reducing Na+ flux from root to leaves, increasing amino acid content and strengthening antioxidant metabolism. Endogenous GABA content was induced by salt and exogenous GABA at both the transcriptional and metabolic levels.
γ-Aminobutyric acid (GABA) participates in the regulation of adaptability to abiotic stress in plants. The objectives of this study were to investigate the effects of GABA priming on improving thermotolerance in creeping bentgrass (Agrostis stolonifera) based on analyses of physiology and proteome using iTRAQ technology. GABA-treated plants maintained significantly higher endogenous GABA content, photochemical efficiency, performance index on absorption basis, membrane stability, and osmotic adjustment (OA) than untreated plants during a prolonged period of heat stress (18 days), which indicated beneficial effects of GABA on alleviating heat damage. Protein profiles showed that plants were able to regulate some common metabolic processes including porphyrin and chlorophyll metabolism, glutathione metabolism, pyruvate metabolism, carbon fixation, and amino acid metabolism for heat acclimation. It is noteworthy that the GABA application particularly regulated arachidonic acid metabolism and phenylpropanoid biosynthesis related to better thermotolerance. In response to heat stress, the GABA priming significantly increased the abundances of Cu/ZnSOD and APX4 that were consistent with superoxide dismutase (SOD) and ascorbate peroxidase (APX) activities. The GABA-upregulated proteins in relation to antioxidant defense (Cu/ZnSOD and APX4) for the reactive oxygen species scavenging, heat shock response (HSP90, HSP70, and HSP16.9) for preventing denatured proteins aggregation, stabilizing abnormal proteins, promoting protein maturation and assembly, sugars, and amino acids metabolism (PFK5, ATP-dependent 6-phosphofructokinase 5; FK2, fructokinase 2; BFRUCT, β-fructofuranosidase; RFS2, galactinol-sucrose galactosyltransferase 2; ASN2, asparagine synthetase 2) for OA and energy metabolism, and transcription factor (C2H2 ZNF, C2H2 zinc-finger protein) for the activation of stress-defensive genes could play vital roles in establishing thermotolerance. Current findings provide an illuminating insight into the new function of GABA on enhancing adaptability to heat stress in plants.
The diversity of secondary compounds in the plant kingdom is huge. About 200,000 compounds are known, which are grouped into amines, non-protein amino acids, peptides, alkaloids, glucosinolates, cyanogenic glucosides, organic acids, terpenoids, quinones, polyacetylenes, and phenolics. The group of phenolic compounds consists of polyphenols, oligophenols and monophenols or simple phenolic compounds such as benzoic and cinnamic acids and their hydroxylated derivatives. Among the thousands of compounds present in ecological interactions, simple phenolic acids are the most abundant in soils, and many are described as allelochemicals. Given the physiological and biochemical importance of these compounds, we review their biosynthesis and metabolic actions in plants.
In order to investigate the physiological effects of exogenous γ-aminobutyric acid (GABA) on drought tolerance in white clover (Trifolium repens), GABA shunt, polyamines (PAs), and proline (Pro) metabolism were examined after plants pretreated with or without GABA (8 mM) and then exposed to water or 15% PEG-induced drought stress in growth chamber. In this study, exogenous application of GABA effectively alleviated drought-induced damage in leaves, as reflected by significantly higher relative water content, lower electrolyte leakage, lipid peroxidation, and leaf wilt. Exogenous GABA further promoted drought-induced increases in GABA transaminase and alpha ketone glutarate dehydrogenase activities, but inhibited glutamate decarboxylase activity under both control and drought conditions, resulting in an increase in endogenous glutamate (Glu) and GABA content. Besides, exogenous GABA could well accelerated PAs synthesis and suppressed PAs catabolism, which lead to the extremely enhanced different types of PAs content (free Put and Spd, insoluble bound Spd and Spm, soluble conjugated Spd and Spm, and total Put, Spd and Spm) under drought stress. In addition, exogenous GABA application further activated drought-induced Δ¹-pyrroline-5-carboxylate synthetase and proline dehydrogenase activities, but suppressed drought-facilitated ornithine -δ-amino transferase activities, leading to a higher Pro accumulation and metabolism in GABA-pretreated plants in the middle and last period of drought. The results suggested that increased endogenous GABA by exogenous GABA treatment could improve drought tolerance of white clover associated with a positive regulation in the GABA-shunt, PAs and Pro metabolism.
Decoration of phytochemicals contributes to the majority of metabolic diversity in nature, whereas how this process alters the biological functions of their precursor molecules remains to be investigated. Flavones, an important yet overlooked subclass of flavonoids, are most commonly conjugated with sugar moieties by UDP-dependent glycosyltransferases (UGTs). Here, we report that the natural variation of rice flavones is mainly determined by OsUGT706D1 (flavone 7-O-glucosyltransferase) and OsUGT707A2 (flavone 5-O-glucosyltransferase). UV-B exposure and transgenic evaluation demonstrate that their allelic variation contributes to UV-B tolerance in nature. Biochemical characterization of over 40 flavonoid UGTs reveals their differential evolution in angiosperms. These combined data provide biochemical insight and genetic regulation into flavone biosynthesis and additionally suggest that adoption of the positive alleles of these genes into breeding programs will likely represent a potential strategy aimed at producing stress-tolerant plants.
Global climate change represents a moving target for plant acclimation and/or adaptation,
especially in the Mediterranean basin. In this study, the interactions of severe drought (20% of the
effective daily evapotranspiration) and O3 fumigation (80 ppb, 5 h day−1, for 28 consecutive days)
on (i) photosynthetic performance, (ii) cell membrane stability, (iii) hydric relations, (iv)
accumulation of compatible solutes, and (v) lipophilic antioxidant compounds were investigated in
young Quercus cerris plants. In addition to the typical drought‐induced stomatal closure, imposition
of water withholding dramatically influenced the profile of stress‐associated metabolites, i.e.,
abscisic acid (ABA), proline, and lipophilic antioxidants. However, plants were not able to delay or
prevent the negative effects of water deficit, the greatest impacting factor in this study. This
translated into a steep decline of photosynthetic efficiency, leaf hydration, and membrane fluidity
and permeability. When water stress was coupled with O3, plants orchestrated cross‐talk among
ABA, proline, and sugar in fully‐expanded mature leaves, partially leading to a premature
senescence.
Liriodendron tulipifera (known as the tulip tree) is a woody species that has been previously classified as sensitive to ozone (O3) in terms of visible leaf injuries and photosynthetic primary reactions. The objective of this work is to give a thorough description of the detoxification mechanisms that are at the basis of O3 sensitivity. Biochemical and molecular markers were used to characterize the response of 1-year-old saplings exposed to O3 (120?ppb, 5?h?day(-1), for 45 consecutive days) under controlled conditions. O3 effects resulted in a less efficient metabolism of Halliwell-Asada cycle as confirmed by the diminished capacity to convert the oxidized forms of ascorbate and glutathione in the reduced ones (AsA and GSH, respectively). The reduced activity of AsA and GSH regenerating enzymes indicates that de novo AsA biosynthesis occurred. This compound could be a cofactor of several plant-specific enzymes that are involved in the early part of the phenylpropanoid and flavonoid biosynthesis pathway, as confirmed by the significant rise of PAL activity (+75%). The induction of the defence-related secondary metabolites (in particular, rutin and caffeic acid were about threefold higher) and the concomitant increase in transcript levels of PAL and CHS genes (+120 and 30%, respectively) suggest that L. tulipifera utilized this route in order to partially counteract the O3-induced oxidative damage.
Physiological and biochemical responses to ozone (O3) (150 ppb, 8 h day⁻¹, 35 consecutive days) of two Italian provenances (Piedmont and Tuscany) of Fraxinus excelsior L. were evaluated, with special attention to the role of phenylpropanoids. Our results indicate (i) the high O3 sensitivity especially of Piedmont provenance (in terms of visible injury, water status, and photosynthetic apparatus); (ii) although the intra-specific sensitivity to O3 between provenances differs (mainly due to different stomatal behaviors since only Tuscany plants partially avoided the uptake of the pollutant gas), both provenances showed detoxification and defense mechanisms; (iii) the crucial participation of phenylpropanoids, with a key role played by flavonoids (especially quercitrin): among this class of metabolites, isoquercitrin is the principal player in the lower O3 sensitivity of Tuscany plants, together with lignins; (iv) although coumarins (typical compounds of Fraxinus) were severely depressed by O3, isofraxidin was triggered suggesting a key role in reactive oxygen species (ROS) detoxification, as well as trans-chalcone. Furthermore, the different behavior of verbascoside and oleuropein among provenances lead us to speculate on their influence in the tentatively repair or acclimation shown by Piedmont plants at the end of the exposure. Finally, the intra-specific O3 sensitivity may be also due to de novo peaks triggered by O3 not yet associated to some chemicals.
Rice (Oryza sativa L.) is one of the most important cereals grown worldwide, mostly in warm regions. However, cold temperature is a major environmental factor that limits rice cultivation in temperate climates. γ-Aminobutyric acid (GABA), glutamic acid (Glu), and calcium chloride (CaCl2) play significant roles in key regulatory pathways throughout plant development. Here, we investigated the effects of Glu, CaCl2, and GABA in the culture medium on the cold tolerance of rice at the seedling stage. The medium components for cold tolerance of rice were optimized using response surface methodology (RSM). Plants treated with cold stress alone (without Glu, CaCl2, or GABA applications) displayed decreased weight, lower relative water content (RWC), maximum photochemical efficiency of PSII (Fv/Fm) and PSII efficiency, and higher relative electrolyte leakage (REL). However, after application of Glu, CaCl2, and GABA, the opposite results were documented, which could be due to an alleviation of cold-induced effects by restoration of membrane integrity. However, the levels of REL were considerably decreased due to Glu, CaCl2, and GABA treatment. RWC, Fv/Fm, PSII efficiency, and the average of subordinate functional values (ASFV) increased with the addition of Glu, CaCl2 and GABA. A central composite design indicated that the optimal concentrations of culture components for the cold tolerance of rice were 2.21 mg/mL, 2.94 mM and 2.68 mM of Glu, CaCl2, and GABA, respectively, and the maximal ASFV (0.987) was obtained under optimal conditions. Analysis of variance for the regression model suggested that the model can predict exactly the cold tolerance of rice seedlings, and the optimal culture components can be used to enhance the cold tolerance of rice seedlings.
Reactive oxygen species (ROS), including superoxide (O2 (.-) /HO2 (.) ) and hydrogen peroxide (H2 O2 ), are differentially produced during resistance responses to biotrophic pathogens and during susceptible responses to necrotrophic and hemi-biotrophic pathogens. Superoxide dismutase (SOD) is responsible for catalysing the dismutation of O2 (.-) /HO2 (.) to H2 O2 regulating the redox status of plant cells. Increased SOD activity has been previously correlated with resistance in barley to the hemi-biotrophic pathogen Pyrenophora teres f. teres (Ptt, the causal agent of net form of net blotch disease) but the role of individual isoforms of SOD has not been studied. A cytosolic CuZnSOD, HvCSD1, was isolated from barley and characterised as being expressed in tissue from different developmental stages. HvCSD1 was upregulated during the interaction with Ptt and to a greater extent during the resistance response. Net blotch disease symptoms and fungal growth were not as pronounced in transgenic HvCSD1 knockdown lines in a susceptible background (cv. Golden Promise), as compared to wild type plants, suggesting that cytosolic O2 (.-) /HO2 (.) contributes to the signalling required to induce a defence response to Ptt. There was no effect of HvCSD1 knockdown on infection by the hemi-biotrophic rice blast pathogen Magnaporthe oryzae or the biotrophic powdery mildew pathogen, Blumeria graminis f. sp. hordei but HvCSD1 also played a role in the regulation of lesion development by methyl viologen. Together these results suggest that HvCSD1 could be important in maintaining cytosolic redox status and in the differential regulation of responses to pathogens with different lifestyles. This article is protected by copyright. All rights reserved.
The non-proteinogenic amino acid γ-aminobutyric acid (GABA) is present in all organisms analyzed so far. In invertebrates GABA acts as a neurotransmitter; in plants different functions are under discussion. Among others, its involvement in abiotic stress reactions and as a defensive compound against feeding insects is suggested. GABA is synthesized from glutamate by glutamate decarboxylases and degraded by GABA-transaminases. Here, in Arabidopsis thaliana, gad1/2 double mutants showing reduced GABA concentrations as well as GABA-enriched triple mutants (gad1/2 x pop2-5) were generated and employed for a systematic study of GABA induction, accumulation and related effects in Arabidopsis leaves upon herbivory. The results demonstrate that GABA accumulation is stimulated by insect feeding-like wounding by a robotic caterpillar, MecWorm, as well as by real insect (Spodoptera littoralis) herbivory. Higher GABA levels in both plant tissue and artificial dietary supplements in turn affect the performance of feeding larvae. GABA enrichment occurs not only in the challenged but also in adjacent leaf. This induced response is neither dependent on herbivore defense-related phytohormones, jasmonates, nor is jasmonate induction dependent on the presence of GABA. Thus, in Arabidopsis the rapid accumulation of GABA very likely represents a general, direct and systemic defense reaction against insect herbivores.
The non-protein amino acid, gamma-aminobutyric acid (GABA) rapidly accumulates in plant tissues in response to biotic and abiotic stress, and regulates plant growth. Until now it was not known whether GABA exerts its effects in plants through the regulation of carbon metabolism or via an unidentified signalling pathway. Here, we demonstrate that anion flux through plant aluminium-activated malate transporter (ALMT) proteins is activated by anions and negatively regulated by GABA. Site-directed mutagenesis of selected amino acids within ALMT proteins abolishes GABA efficacy but does not alter other transport properties. GABA modulation of ALMT activity results in altered root growth and altered root tolerance to alkaline pH, acid pH and aluminium ions. We propose that GABA exerts its multiple physiological effects in plants via ALMT, including the regulation of pollen tube and root growth, and that GABA can finally be considered a legitimate signalling molecule in both the plant and animal kingdoms.
γ-Aminobutyric acid (GABA) is a non-proteinogenic amino acid that is found in uni- and multi-cellular organisms and is involved in many aspects of plant life cycle. GABA metabolism occurs by the action of evolutionary conserved enzymes that constitute the GABA shunt, bypassing two steps of the TCA cycle. The central position of GABA in the interface between plant carbon and nitrogen metabolism is well established. In parallel, there is evidence to support a role for GABA as a signaling molecule in plants. Here we cover some of the recent findings on GABA metabolism and signaling in plants and further suggest that the metabolic and signaling aspects of GABA may actually be inseparable.
Tropospheric ozone (O3) concentrations are rising in Indo-Gangetic plains of India, causing potential threat to agricultural productivity. Maize (Zea mays L.) is the third most important staple crop at global level after rice and wheat. Two high yielding cultivars of Indian maize (HQPM1-quality protein maize and DHM117-normal/non quality protein maize) were exposed to two levels of elevated O3 above the ambient level (NFC) viz. NFC + 15 ppb O3 (NFC + 15) and NFC + 30 ppb O3 (NFC + 30) using open top chambers under field conditions. The study was conducted to evaluate the biochemical responses of two cultivars at different developmental stages leading to change in yield responses. Initially at lower O3 dose, photosynthetic pigments showed an increase but reduction at later stage, while higher dose caused a decline at both the stages of sampling. Levels of superoxide radical (O2
−) and hydrogen peroxide (H2O2) significantly increased and contributed to lipid peroxidation at elevated O3. Histochemical localization assay of O2
− and H2O2 showed that guard cells of stomata and cells around trichomes took deeper stain at elevated O3 reflecting more formation of reactive oxygen species. Secondary metabolites like total phenol, flavonoids and anthocyanin pigments also increased in plants under O3 stress. Enzymatic antioxidants were triggered in both the cultivars due to elevated O3, while induction of non-enzymatic antioxidants was more in HQPM1. Native PAGE analysis also showed that SOD, POX, CAT, APX and GPX were stimulated at elevated O3 concentrations compared to NFC. SDS-PAGE showed reductions of major photosynthetic proteins with higher decrease in DHM117. Principal Component Analysis showed that both the cultivars showed differential response against O3 at two developmental stages. HQPM1 maintained the analogous defense strategy at both the sampling stages while DHM117 showed variable response. Overall metabolic induction of antioxidants related to defense was more in DHM117 than HQPM1. This suggests that DHM117 utilized more assimilates in maintaining the homeostasis against imposed oxidative stress, causing less translocation of assimilates to reproductive parts and thus affecting the final yield. In terms of yield it is suggested that performance of HQPM1 (quality protein maize) was better than the DHM117 (non quality protein maize).
Plants of 16 Italian cultivars of durum wheat at the tillering stage were exposed to
a single pulse of ozone (O3, 200 ppb, 5 h day−1) to reveal the mechanisms explaining their O3 tolerance/sensitivity by considering some leaf physiochemical traits [e.g., stomatal conductance, photosystem II (PSII) efficiency, antioxidant enzyme activity, and phytohormone synthesis]. At the end of the recovery period (48 h from the beginning of the exposure), all cultivars showed visible foliar injury in the form of widespread chlorosis which developed in bifacial ivory necrotic lesions scattered among the leaf veins of completely expanded leaves. Mongibello leaves showed not only the highest severity of visible injury (McKinney index = 62%), but also a reduction of PSII performance (Fv/Fm ratio: −22% compared with controls) together with an activation of the dissipation of the excess excitation energy as heat (qNP: +35%). The photosynthetic impairment observed throughout the whole experiment, was likely due to stomatal limitations (gs: −36% as average) and indicated that this cultivar was very sensitive to a pulse of O3. Similar results were obtained for Latino and Meridiano. Conversely, Iride, Orobel, and Portorico showed the lowest severity of visible injury (McKinney index around 13%) suggesting that they could be considered tolerant to a pulse of O3. These cultivars showed none or only transient changes due to O3 in terms of photosynthetic activity (e.g., A values), while the slight decrease of Fv/Fm ratio did not determine the photoinhibition of the PSII activity, since mechanisms for dissipating excess excitation energy were being activated. Ozone treatment induced a significant reduction of CO2 assimilation rate (−34%) in Orobel and this is not attributable to stomatal and non-stomatal limitations. The remaining cultivars were considered moderately sensitive
to O3, with McKinney index in the range of 20–43%. The measured biochemical
traits are not decisive in determining the O3 sensitivity. In particular, the activity
of phenylalanine ammonia lyase increased only in seven cultivars; among them, only
in Latino, Vetrodur, and Simeto, this enhancement reflected in an accumulation of
phenolic compounds suggesting potential higher protection against reactive oxygen
species. This work highlights the relevance of identifying O3-sensitive cultivars, in the optic to develop sustainable strategies to mitigate the impact of peak O3 episodes on wheat production.
Elevated levels of tropospheric ozone (O3) are phytotoxic, inhibiting plant growth and production and, thus, compromising environmental health and sustainable crop production. It is therefore critical to devise strategies to protect plants from the negative effects of O3. However, the efficacy of the different chemical or non-chemical methods to protect plants against O3 toxicities has not been critically reviewed. Hence, this study aimed at comprehensively reviewing various methods of crop protection against O3 stress. Ethylenediurea (EDU) is the most investigated and efficient protectant in ameliorating O3-induced phytodamage. However, plant protectants (e.g. pesticides, fungicides), antitranspirants (e.g. di-1-p-menthene), antioxidants (e.g. ascorbic acid, diphenylamine), exogenously-applied plant hormones (e.g. ethylene, kinetin, abscisic acid), and nutrient management strategies (e.g. varied level of nitrogen fertilizers, application of calcium acetate) were also found to offer some protection against O3. Hence, more studies are needed to comprehensively explore the potential of these methods, individually and in different combinations. Biological mechanisms that underlie the ameliorative effect of the different methods are discussed along with the relevance of the concept of hormesis. This assessment also acknowledges major information gaps and suggests future options for dealing with O3 pollution. New insights into the efficacy of additional protectants provide a new dimension to plant protection against O3-induced detrimental effects, and suggest that future research should use a green chemistry approach and an ‘one health’ perspective.
In recent years, surface ozone concentrations have increased in many cities in China. Ground-based multi-axis differential optical absorption spectroscopy (MAX-DOAS) is a powerful technique for retrieving the profiles of tropospheric trace gases, such as NO2, SO2, and HCHO. However, since the difficulties in deducting the effects of stratospheric ozone, there are few studies on the retrieval of tropospheric ozone profiles using MAX-DOAS measurements. Here, we developed an accurate inversion method to retrieve tropospheric ozone concentrations during the PRIDE-GBA Campaign, wherein the ozone differential slant column densities (DSCDs) were retrieved in QDOAS software using the "time-interpolated zenith spectrum" as the reference spectrum. The tropospheric DSCDs (DSCDstrop) were then calculated by subtracting the simulated stratospheric DSCDs (DSCDsstr, simulated from the SCIATRAN model) from the DSCDs. Tropospheric ozone profiles were retrieved from the DSCDstrop using the optimal estimation method (OEM). The results showed that high values of tropospheric ozone were mainly distributed below 1 km, which is consistent with lidar measurements. In addition, the observed surface ozone concentrations were highly correlated with the in-situ measurements, with correlation coefficients (R) of 0.75 and 0.81, respectively. Combined with the retrieved NO2 and HCHO profiles using the MAX-DOAS measurements, we found that the planetary boundary layer ozone pollution of HeShan Observatory during the PRIDE-GBA Campaign are controlled by the NOx-limited regime. The results of this study indicate that the MAX-DOAS technique has the potential to retrieve tropospheric ozone profiles with high temporal and spatial resolution.
γ-Aminobutyric acid (GABA), a signal molecule, is regarded as the intersection node of carbon and nitrogen metabolism, and its contributions to flavonoid metabolism in tea plant growth and development remain unclear. The correlation between the GABA shunt and flavonoid metabolism in tea plants is worth to explore. Secondary metabolites and their correlations with the taste of tea soup made from tea plants (Camellia sinensis) during different seasons were investigated. Related secondary metabolites and transcript profiles of genes encoding enzymes in the GABA shunt, flavonoid pathway and polyamine biosynthesis were measured throughout the tea plant growth seasons and after exogenous GABA applications. In addition, the abundance of differentially expressed proteins was quantified after treatments with or without exogenous GABA. The tea leaves showed the highest metabolite concentrations in spring season. CsGAD, CsGABAT, CsSPMS, CsODC, CsF3H and CsCHS were found to be important genes in the GABA and anthocyanin biosynthesis pathways. GABA and anthocyanin concentrations showed a positive correlation, to some extent, CsF3H and CsCHS played important roles in the GABA and anthocyanin biosynthesis.
As essential source for human consumption, plants of wheat and rice are highly sensitive to ozone (O3), resulting in significant agricultural losses under O3 pollution. According to our results, photosynthesis and shoot biomass of wheat and rice were significantly reduced under elevated O3. The activities of SOD, POD and CAT were responsive to O3 pollution in two crops. However, little is known about the effects of elevated O3 concentration on their metabolite profiling. The response of metabolites to elevated ozone was investigated in model cultivars of wheat and rice. A total of 172 compounds significantly changed in seedlings of wheat (103) and rice (89) under O3 pollution. The strong up-regulation of phospholipids and markedly declined of fatty acids were detected in wheat and rice under elevated O3. Methylerythritol 4-phosphate pathway was altered in both crops with reduced accumulation of carbon compound terpene under O3 stress. Meanwhile, O3 treatment led to the high levels of aspartate-derived asparagine or aspartate, which regulated carbon and nitrogen metabolism. Additionally, O3 suppressed the generation of environmental stress-related flavonoids and cinnamic acids via shikimate pathway in the two crops. Moreover, the biosynthesis of sterols was suppressed and isocitrate was not changed under ozone fumigation in wheat, while both of them were increased in rice. The metabolic results reveal the involvement of O3-related metabolites in photosynthesis, oxidative stress and carbon/nitrogen balance. Our findings provide valuable information for understanding of ozone's effects on the physiology and metabolite profiling of crop plants, boosting efforts to screen genetic resources for valuable traits to adapt to O3 pollution.
Current ozone (O3) concentration levels entail significant damages in crop yields around the world. The reaction of the emitted precursors (mostly methane and nitrogen oxides) with solar radiation contribute to O3 levels that exceed established thresholds for crop damage. This paper shows current and projected (up to 2080) relative yield losses (RYLs) driven by O3 exposure for different crops and the associated economic damages applying dynamic crop production and prices that are calculated per region and period. We adjust future crop yields in the Global Change Assessment Model (GCAM) to reflect the RYLs and analyze the effects on agricultural markets. We find that the changes (generally reductions) in O3 precursor emissions in a reference scenario would reduce the agricultural damages, compared to present, for most of the regions, with a few exceptions including India, where higher future O3 concentrations have large negative impacts on crop yields. The annual economic impact of O3 driven losses from 2010 to 2080 are, in billion US dollars at 2015 prices ($B), 5.0–6.0, 9.8–18.8, 6.7–10.6 and 10.4–12.5 for corn, soybeans, rice and wheat, respectively, with the large losses for wheat and soybeans driven by their comparatively high responses to O3. When O3 effects are explicitly modelled as exogenous yield shocks in future periods, there is a direct impact in future agricultural markets. Therefore, the aggregated net present value (NPV) of crop production would be reduced around by $90.8 B at a global level. However, these changes are not distributed evenly across regions, and the net present market value of the crops would increase by up to $118.2 B (India) or decrease by up to $59.2 B (China).
γ-Aminobutyric acid (GABA), a non-proteinaceous amino acid, modulates plant growth and stress tolerance. However, the potential role of GABA in regulating key metabolic pathways and stress-defensive proteins against drought in plants has never been explored. Creeping bentgrass (Agrostis stolonifera) plants were pretreated with or without GABA and then subjected to water stress for 8 days in controlled growth chambers (23/19 °C, day/night). Physiological analysis showed that elevated endogenous GABA level via exogenous GABA application significantly mitigated water stress damage to creeping bentgrass, as manifested by increased leaf relative water content, water use efficiency, osmotic adjustment (OA), photochemical efficiency (Fv/Fm), net photosynthetic rate, and reduced oxidative damage. iTRAQ-based proteomics found that enhanced chaperones accumulation, carbohydrates, amino acids, and energy metabolism played important roles in protein protection, OA, energy maintenance, and metabolic balance, which is important adaptive response to drought stress in creeping bentgrass. The GABA further promoted energy production and conversion, antioxidant defense, and DHN3 accumulation that were essential for energy requirement, ROS-scavenging, and the prevention of cell dehydration in leaf during drought stress. In addition, GABA-treated plants maintained significantly higher abundance of dicarboxylate transporter 2.1, ATP-dependent zinc metalloprotease, receptor-like protein kinase HERK1, o-acyltransferase WSD1, omega-6 fatty acid desaturase, and two-component response regulator ORR21 than untreated plants under drought stress. The result provides new evidences that GABA-induced drought tolerance is possibly involved in the improvement of nitrogen recycling, protection of photosystem II, mitigation of drought-depressed cell elongation, wax biosynthesis, fatty acid desaturase, and delaying leaf senescence in creeping bentgrass.
γ-Aminobutyric acid (GABA) is an important neurotransmitter in mammals whose receptor is reported to be regulated by flavonoids. In plants, it is considered to be at the intersection of carbon and nitrogen metabolism, but its relationship with flavonoid metabolism remains unclear. Our recent RNA-seq analysis showed that expression of flavonoid biosynthetic genes was influenced in poplar by the blockage of α-ketoglutarate dehydrogenase (α-KGDH) activity and the application of GABA under NaCl stress, accompanied by the changes in GABA shunt activity. Here, we further found that the flavonoid accumulation was significantly affected by blocking the activities of α-KGDH and GABA transaminase as well as applying exogenous GABA, coupled with the changes of endogenous GABA contents. Key genes involved in the flavonoid biosynthetic pathway were also significantly influenced, including two PALs, 4CL, and two CHSs. Our results suggest that the GABA shunt is closely associated with the metabolism of flavonoids, which would benefit future understanding of GABA’s roles in carbon allocation by regulating the pathway of flavonoid biosynthesis under normal or stress conditions.
Plants are frequently exposed to adverse environmental conditions such as drought and ozone (O3). Under these conditions, plants can survive due to their ability to adjust their metabolism. The aim of the present study was to compare the detoxification mechanisms of three oak species showing different O3 sensitivity and water use strategy. Two-year-old seedlings of Quercus ilex, Q. pubescens and Q. robur were grown under the combination of three levels of O3 (1.0, 1.2 and 1.4 times the ambient O3 concentration) and three levels of water availability (on average 100, 80 and 42% of field capacity i.e. well-watered, moderate drought and severe drought, respectively) in an O3 Free Air Controlled Exposure facility. Ozone and drought induced the accumulation of reactive oxygen species (ROS) and this phenomenon was species-specific. Sometimes, ROS accumulation was not associated with membrane injury suggesting that several antioxidative defence mechanisms inhibited or alleviated the oxidative damage. Both O3 and drought increased total carotenoids that were able to prevent the peroxidation action by free radicals in Q. ilex, as confirmed by unchanged malondialdehyde by-product values. The concomitant decrease of total flavonoids may be related to the consumption of these compounds by the cell to inhibit the accumulation of hydrogen peroxide. Unchanged total phenols confirmed that Q. ilex has a superior ability to counteract oxidative conditions. Similar responses were found in Q. pubescens, although the negative impact of both factors was less efficiently faced than in the sympatric Q. ilex. In Q. robur, high O3 concentrations and severe drought induced a partial rearrangement of the phenylpropanoid pathways. These antioxidative mechanisms were not able to protect the cell structure (as confirmed by ROS accumulation) suggesting that Q. robur showed a lower degree of tolerance than the other two species.
In plants, γ-aminobutyric acid (GABA) accumulates rapidly in response to environmental stress and variations in its endogenous concentration have been shown to affect plant growth. Exogenous application of GABA has also conferred higher stress tolerance by modulating the expression of genes involved in plant signalling, transcriptional regulation, hormone biosynthesis, reactive oxygen species production and polyamine metabolism. Plant hormones play critical roles in adaptation of plants to adverse environmental conditions through a sophisticated crosstalk among them. Several studies have provided evidence for the relationships between GABA, polyamines and hormones such as abscisic acid, cytokinins, auxins, gibberellins and ethylene, among others, focussing on the effect that one specific group of compounds exerts over the metabolic and signalling pathways of others. In this review, we bring together information obtained from plants exposed to several stress conditions and discuss the possible links among these different groups of molecules. The analysis supports the view that highly conserved pathways connect primary and secondary metabolism, with an overlap of regulatory functions related to stress responses and tolerance among phytohormones, amino acids and polyamines.
We review current knowledge of the processes by which ozone will cause injury and damage in crop plants. We do this both through an understanding of the limitations to ozone uptake (i.e. ozone being transferred from some height in the atmosphere to the leaf boundary layer and subsequent uptake via the stomata) as well as through the internal plant processes that will result in damage and /or injury. We consider these processes across the range of scales that are impacted in the plant, from cellular injury and damage (that can result in visible injury and alterations to photosynthesis and stomatal conductance) through to leaf level impacts on physiology and leaf senescence and ultimately to alterations in whole plant canopy and root systems that will affect biogeochemical cycling within the plant. We consider these processes from the viewpoint of developing crop growth models that are capable of incorporating key ozone impact processes within modelling structures that asses crop growth under a variety of different stresses. This would provide a dynamic assessment of the impact of ozone on crop growth within the context of other key variables considered important in determining crop growth and yield. We consider the ability to achieve this through an assessment of the different types of crop model (e.g. empirical, radiation use efficiency, and photosynthesis based crop growth models. Finally, we show how international activities such as the AgMIP (Agricultural Modelling and Improvement Intercomparison Project) could provide a network of crop growth modellers to assess the capabilities of different crop models to simulate the effects of ozone and other stresses to improve future regional and global risk assessments.
Introduction of high‐performing crop cultivars and crop/soil water management practices that increase the stomatal uptake of carbon dioxide and photosynthesis will be instrumental in realizing the United Nations Sustainable Development Goal (SDG) of achieving food security. To date, however, global assessments of how to increase crop yield have failed to consider the negative effects of tropospheric ozone, a gaseous pollutant that enters the leaf stomatal pores of plants along with carbon dioxide, and is increasing in concentration globally, particularly in rapidly developing countries. Earlier studies have simply estimated that the largest effects are in the areas with the highest ozone concentrations. Using a modelling method that accounts for the effects of soil moisture deficit and meteorological factors on the stomatal uptake of ozone, we show for the first time that ozone impacts on wheat yield are particularly large in humid rain‐fed and irrigated areas of major wheat‐producing countries (e.g. USA, France, India, China and Russia). Averaged over 2010‐2012, we estimate that ozone reduces wheat yields by a mean 9.9% in the northern hemisphere and 6.2% in the southern hemisphere, corresponding to some 85 Tg (million tonnes) of lost grain. Total production losses in developing countries receiving Official Development Assistance are 50% higher than those in developed countries, potentially reducing the possibility of achieving UN SDG2. Crucially, our analysis shows that ozone could reduce the potential yield benefits of increasing irrigation usage in response to climate change because added irrigation increases the uptake and subsequent negative effects of the pollutant. We show that mitigation of air pollution in a changing climate could play a vital role in achieving the above‐mentioned UN SDG, whilst also contributing to other SDGs related to human health and wellbeing, ecosystems and climate change.
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In the natural environment, plants are exposed to a variety of biotic and abiotic stress conditions that trigger rapid changes in the production and scavenging of reactive oxygen species (ROS). The production and scavenging of ROS is compartmentalized, which means that, depending on stimuli type, they can be generated and eliminated in different cellular compartments such as the apoplast, plasma membrane, chloroplasts, mitochondria, peroxisomes, and endoplasmic reticulum. Although the accumulation of ROS is generally harmful to cells, ROS play an important role in signaling pathways that regulate acclimatory and defense responses in plants, such as systemic acquired acclimation (SAA) and systemic acquired resistance (SAR). However, high accumulations of ROS can also trigger redox homeostasis disturbance which can lead to cell death, and in consequence, to a limitation in biomass and yield production. Different ROS have various half-lifetimes and degrees of reactivity toward molecular components such as lipids, proteins, and nucleic acids. Thus, they play different roles in intra- and extra-cellular signaling. Despite their possible damaging effect, ROS should mainly be considered as signaling molecules that regulate local and systemic acclimatory and defense responses. Over the past two decades it has been proven that ROS together with non-photochemical quenching (NPQ), hormones, Ca2+ waves, and electrical signals are the main players in SAA and SAR, two physiological processes essential for plant survival and productivity in unfavorable conditions.
Water deficit is an abiotic stress factor that negatively affects black cumin (Nigella sativa L.) production. Gamma aminobutyric acid (GABA), an endogenous signaling molecule and metabolite, has high physiological and molecular activity in plant cells, which can promote tolerance to water deficit stress, but little information is available on the effect of exogenous application on growth of black cumin. A field experiment over two years was carried out at Urmia University, West Azerbaijan, Iran to evaluate the effects of GABA on some agronomic and biochemical attributes of black cumin under water deficit stress conditions. Three irrigation treatments (irrigation after 50, 100, and 150 mm evaporation based on evaporation from class A pan) and four levels of GABA application (0, 0.5, 1.0 and 2.0 mg L-1) were tested. Irrespective of GABA application, the severe water deficit treatment (i.e., irrigation after 150 mm evaporation) provided the lowest seed number per follicle, 1000-seed weight, and seed yield. Increasing water deficit, significantly reduced chlorophyll a by 7.8 to 16.7% and chlorophyll b by 9.8 to 19.1%, whereas GABA application significantly improved these traits. The application of 2.0 mg L-1 GABA increased chlorophyll a content by 6.4% and chlorophyll b content by 21.1% compared with control. In addition, GABA application showed a positive and significant effect on soluble sugars content, proline accumulation, and catalase (CAT) activity. The maximum values of these variables were obtained with the application of GABA at 2.0 mg L-1. CAT, peroxidase (POX), and superoxide dismutase (SOD) activity increased with decreasing chlorophyll a and chlorophyll b contents, whereas soluble sugars and proline content increased with increasing activity of those antioxidant enzymes. Overall, in addition to cellular mechanisms, such as osmoregulation and antioxidant defense, GABA application can improve growth and productivity of black cumin under water deficit stress conditions.
Scarcity of water is a severe constraint, which hinders the wheat productivity worldwide. However, foliage application of osmoprotectants may be useful in reducing the drought-induced yield losses in wheat (Triticum aestivum L.). In this study, potential of foliage applied osmoprotectants (proline, gamma-aminobutyric acid) in improving the performance of bread wheat against terminal drought was evaluated. Both proline and gamma-aminobutyric acid (GABA) were foliage applied at 50, 100 and 150 mg/L at anthesis stage (BBCH-identification code- 61), in two bread wheat cultivars viz. Mairaj-2008 and BARS-2009. After 1 week of foliage application of these osmoprotectants, drought was imposed by maintaining the pots at 35% water holding capacity. Imposition of drought caused significant reduction in the grain yield of both tested bread wheat cultivars; nonetheless, foliage applied osmoprotectants at either concentration improved the chlorophyll contents, accumulation of proline, glycinebetaine and total soluble phenolics and reduced the malondialdehyde contents, which resulted in better stay green, maintenance of grain weight and grain number under drought stress, thus resulting in better grain yield, water-use efficiency and transpiration efficiency in both wheat cultivars. However, foliage applied proline at 150 mg/L, and GABA at 100 mg/L was most effective than other concentrations of these osmoprotectants. Performance of cultivar Mairaj-2008 was quite better than cultivar BARS-2009. In crux, foliar application of proline and GABA at pre-optimized rate can be opted as a shotgun approach to improve the performance of wheat under terminal drought.
γ-Aminobutyric acid (GABA) accumulates rapidly when plants are exposed to stress. Whether GABA accumulation represents the regulation of metabolism in response to stress or an adaptive response to mitigate stress is unknown. Genetic manipulation of GABA levels has revealed that GABA accumulation functions in defense against drought and insect herbivory.
Gama-aminobutyric acid (GABA) is a nonprotein amino acid in plant cells, which responds to changes in environmental factors. The objectives of this study were to evaluate the effects of foliar spray of GABA on drought and heat tolerance in creeping bentgrass (Agrostis stolonifera), and to investigate physiological factors altered by GABA application that contribute to improved drought tolerance and heat tolerance. GABA-treated plants (cv. Penncross) or non-GABA-treated control plants were then subjected to the following three treatments in growth chambers: 1) nonstress control [plants irrigated every 2 days to maintain soil water content at the pot capacity and maintained at 21/19 8C (day/night) for 35 days], 2) heat stress [plants exposed to 35/30 8C (day/night) and well-watered conditions for 35 days], and 3) drought stress [plants unirrigated for 9 days and maintained at 21/19 8C (day/night), and then rewatered for 2 days]. As compared with untreated plants, GABA-treated plants showed 22%to 39%and 8%to 21% significantly lower leaf electrolyte leakage (EL) and 35% to 143% and 21% to 24% significantly higher turf quality (TQ), 8%to 17%and 17%to 24%relativewater content (RWC), 22%to 39%and 25%to 27%chlorophyll content, 7% to 11% and 6% to 17% photochemical efficiency, and an 84% to 683% and 57% to 76% osmotic adjustment (OA) exposed to heat or drought stress across days of treatment, respectively. GABA-treated plants accumulated 7% to 10% more water-soluble carbohydrates (WSC) and 11% to 43%more free proline than nontreated plants under heat stress, and 12% to 30% higher accumulation of WSC under drought stress. After 2 days of rewatering, a significantly better recovery also was observed in GABA-treated plants than that in nontreated plants previously exposed to drought stress. The results suggest that foliar application ofGABA significantly improved heat and drought tolerance of creeping bentgrass, which was associated with maintenance of cellmembrane stability, delaying in leaf senescence, and enhancing OA. The effectiveness of exogenous GABA application was more pronounced under heat stress than under drought stress. © 2016, American Society for Horticultural Science. All right reserved.
A rapid accumulation of γ-aminobutyric acid (GABA) during biotic and abiotic stresses is well documented. However, the specificity of the response and the primary role of GABA under such stress conditions are hardly understood. To address these questions, we investigated the response of the GABA-depleted gad1/2 mutant to drought stress. GABA is primarily synthesized from the decarboxylation of glutamate by glutamate decarboxylase (GAD) which exists in five copies in the genome of Arabidopsis thaliana. However, only GAD1 and GAD2 are abundantly expressed, and knockout of these two copies dramatically reduced the GABA content. Phenotypic analysis revealed a reduced shoot growth of the gad1/2 mutant. Furthermore, the gad1/2 mutant was wilted earlier than the wild type following a prolonged drought stress treatment. The early-wilting phenotype was due to an increase in stomata aperture and a defect in stomata closure. The increase in stomata aperture contributed to higher stomatal conductance. The drought oversensitive phenotype of the gad1/2 mutant was reversed by functional complementation that increases GABA level in leaves. The functionally complemented gad1/2 x pop2 triple mutant contained more GABA than the wild type. Our findings suggest that GABA accumulation during drought is a stress-specific response and its accumulation induces the regulation of stomatal opening thereby prevents loss of water.
γ-Aminobutyric acid (GABA) concentration increases rapidly in tissues when plants encounter abiotic or biotic stress, and GABA manipulation affects growth. This, coupled to GABA's well-described role as a neurotransmitter in mammals, led to over a decade of speculation that GABA is a signal in plants. The discovery of GABA-regulated anion channels in plants provides compelling mechanistic proof that GABA is a legitimate plant-signaling molecule. Here we examine research avenues unlocked by this finding and propose that these plant 'GABA receptors' possess novel properties ideally suited to translating changes in metabolic status into physiological responses. Specifically, we suggest they have a role in signaling altered cycling of tricarboxylic acid (TCA) intermediates during stress via eliciting changes in electrical potential differences across membranes.
Gamma-aminobutyric acid (GABA) is a non-protein amino acid that accumulates in a number of plant species under various environmental stresses. In this paper, the ability of applied GABA for the alleviation of NaCl stress was investigated in view of growth parameters, gas exchange, photosynthetic pigments, chlorophyll fluorescence, activities of antioxidant enzymes, malondialdehyde (MDA) content, and electrolyte conductivity (REC) in wheat seedlings. Germination rate and shoot dry mass decreased with an increasing NaCl concentrationand this decrease was less pronounced when 0.5 mM GABA was applied. In the NaCl-treated seedlings, exogenous GABA partially enhanced photosynthetic capacity and antioxidant enzyme activities and decreased MDA content and REC. Therefore, GABA reduced the impact of salinity on the wheat seedlings.
The ubiquitous nonprotein amino acid known as gamma-aminobutyrate (GABA) has been proposed as a mechanism whereby environmental and developmental cues are translocated in phloem. Information about the composition of translocation fluids from various species that bleed spontaneously reveals that GABA is always present in xylem at minor levels, but sometimes absent in phloem. In species that do not bleed spontaneously, GABA is also absent or present at minor levels in aphid stylet exudate. By contrast, GABA in ethylenediaminetetraacetate-facilitated phloem exudates is relatively abundant compared to other amino acids or the concentration of total amino acids present in xylem. Evidence indicates that xylem-borne GABA is primarily retrieved and metabolized by mature leaves, and tissue pools of GABA reflect in situ biosynthesis. Recovery of significant GABA from phloem might be an artifact of wounding and the use of ethylenediaminetetraacetate. Scarce data from aphid stylectomy experiments indicates that GABA is a wound signal. However, the composition of phloem sap collected by this method is not uniform, shedding doubt on some results in the scientific literature. Elevated GABA levels in the host plant are known to influence the success of biotic interactions; however, these outcomes could be attributed to the impact of wounding at local sites, rather than delivery of GABA via phloem. Further research is required to provide unambiguous support for long-distance gamma-aminobutyrate signaling in phloem.
Flavonoids are the low molecular weight polyphenolic secondary metabolic compounds, and have various functions in growth, development, reproduction, and stress defense. However, little is known about the roles of the key enzymes in the flavonoids biosynthesis pathway in response to drought stress in winter wheat. Here, we investigated the expression pattern of flavonoids biosynthesis genes and accumulation of flavonoids in wheat leaves under drought stress. Quantitative real-time PCR analysis showed that there were a rapid increase in expression levels of TaCHS, TaCHI, TaF3H, TaFNS, TaFLS, TaDFR, and TaANS under drought stress in two wheat cultivars Aikang 58 (AK) and Chinese Spring (CS). The cultivar CS exhibited higher genes expression levels of TaCHS, TaCHI, TaF3H, TaFLS, TaDFR, and TaANS, and the cultivar AK showed a higher expression level of TaFNS gene during drought treatment. The increase rates of genes expression were superior in AK compared to CS. Total phenolics content, total flavonoids content, anthocyanin content, and schaftoside content in wheat leaves were enhanced during drought treatment and cultivar CS had a relative higher accumulation. These results suggest that the flavonoids pathway genes expression and accumulation of flavonoids compounds may be closely related to drought tolerant in wheat. Further, flavonoids response mechanism may be different between wheat cultivars.
The present study was conducted to assess morphological, biochemical and yield responses of palak (Beta vulgaris L. cv Allgreen) to ambient and elevated levels of CO(2) and O(3), alone and in combination. As compared to the plants grown in charcoal filtered air (ACO(2)), growth and yield of the plants increased under elevated CO(2) (ECO(2)) and decreased under combination of ECO(2) with elevated O(3) (ECO(2) + EO(3)), ambient O(3) (ACO(2) + AO(3)) and elevated O(3) (EO(3)). Lipid peroxidation, ascorbic acid, catalase and glutathione reductase activities enhanced under all treatments and were highest in EO(3.) Foliar starch and organic carbon contents increased under ECO(2) and ECO(2) + EO(3) and reduced under EO(3) and ACO(2) + AO(3.) Foliar N content declined in all treatments compared to ACO(2) resulting in alteration of C/N ratio. This study concludes that ambient level of CO(2) is not enough to counteract O(3) impact, but elevated CO(2) has potential to counteract the negative effects of future O(3) level.