Gamma-aminobutyric acid (GABA) alleviates salt damage in tomato by modulating Na+ uptake, the GAD gene, amino acid synthesis and reactive oxygen species metabolism.
ABSTRACT: 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.
Project description:The objective of this study was to determine the effect of soaking with ?-aminobutyric acid (GABA) on white clover (Trifolium repens cv. Haifa) seed germination under salt stress induced by 100 mM NaCl. Seeds soaking with GABA (1 ?M) significantly alleviated salt-induced decreases in endogenous GABA content, germination percentage, germination vigor, germination index, shoot and root length, fresh and dry weight, and root activity of seedling during seven days of germination. Exogenous application of GABA accelerated starch catabolism via the activation of amylase and also significantly reduced water-soluble carbohydrate, free amino acid, and free proline content in seedlings under salt stress. In addition, improved antioxidant enzyme activities (SOD, GPOX, CAT, APX, DHAR, GR and MDHR) and gene transcript levels (Cu/ZnSOD, FeSOD, MnSOD, CAT, GPOX, APX, MDHR, GPX and GST) was induced by seeds soaking with GABA, followed by decreases in O??-, H?O?, and MDA accumulation during germination under salt stress. Seeds soaking with GABA could also significantly improve Na?/K? content and transcript levels of genes encoding Na?/K? transportation (HKT1, HKT8, HAL2, H?-ATPase and SOS1) in seedlings of white clover. Moreover, exogenous GABA significantly induced the accumulation of dehydrins and expression of genes encoding dehydrins (SK2, Y2K, Y2SK, and dehydrin b) in seedlings under salt stress. These results indicate that GABA mitigates the salt damage during seeds germination through enhancing starch catabolism and the utilization of sugar and amino acids for the maintenance of growth, improving the antioxidant defense for the alleviation of oxidative damage, increasing Na?/K? transportation for the osmotic adjustment, and promoting dehydrins accumulation for antioxidant and osmotic adjustment under salt stress.
Project description:?-Aminobutyric acid (GABA) has high physiological activity in plant stress physiology. This study showed that the application of exogenous GABA by root drenching to moderately (MS, 150?mM salt concentration) and severely salt-stressed (SS, 300?mM salt concentration) plants significantly increased endogenous GABA concentration and improved maize seedling growth but decreased glutamate decarboxylase (GAD) activity compared with non-treated ones. Exogenous GABA alleviated damage to membranes, increased in proline and soluble sugar content in leaves, and reduced water loss. After the application of GABA, maize seedling leaves suffered less oxidative damage in terms of superoxide anion (O2·-) and malondialdehyde (MDA) content. GABA-treated MS and SS maize seedlings showed increased enzymatic antioxidant activity compared with that of untreated controls, and GABA-treated MS maize seedlings had a greater increase in enzymatic antioxidant activity than SS maize seedlings. Salt stress severely damaged cell function and inhibited photosynthesis, especially in SS maize seedlings. Exogenous GABA application could reduce the accumulation of harmful substances, help maintain cell morphology, and improve the function of cells during salt stress. These effects could reduce the damage to the photosynthetic system from salt stress and improve photosynthesis and chlorophyll fluorescence parameters. GABA enhanced the salt tolerance of maize seedlings.
Project description:The global emergence of soil salinization poses a serious challenge to many countries and regions. γ-Aminobutyric acid (GABA) is involved in systemic regulation of plant adaptation to salt stress, but the underling molecular and metabolic mechanism still remains largely unknown. The elevated endogenous GABA level by exogenous application of GABA could significantly improve salt tolerance in creeping bentgrass with the enhancement of antioxidant capacity, photosynthetic characteristics, osmotic adjustment (OA), and water use efficiency. GABA strongly upregulated transcript levels of AsPPa2, AsATPaB2, AsNHX2/4/6, and AsSOS1/20 in roots involved in enhanced capacity of Na+ compartmentalization and mitigation of Na+ toxicity in cytosol. Significant downregulation of AsHKT1/4 expression could be induced by GABA in leaves in relation to maintenance of significantly lower Na+ accumulation and higher K+/Na+ ratio. GABA-depressed aquaporins (AQPs) expression and accumulation induced declines in stomatal conductance and transpiration, thereby reducing water loss in leaves during salt stress. For metabolic regulation, GABA primarily enhanced sugars and amino acids accumulation and metabolism largely contributing to improved salt tolerance through maintaining OA and metabolic homeostasis. Other major pathways could be responsible for GABA-induced salt tolerance including increases in antioxidant defense, heat shock proteins, dehydrins, and myo-inositol accumulation in leaves. Integrative analyses of molecular, protein, metabolic, and physiological changes reveal systemic function of GABA on regulating ions, water, and metabolic homeostasis in non-halophytic creeping bentgrass under salt stress.
Project description:BACKGROUND:Chitosan (CTS), a natural polysaccharide, exhibits multiple functions of stress adaptation regulation in plants. However, effects and mechanism of CTS on alleviating salt stress damage are still not fully understood. Objectives of this study were to investigate the function of CTS on improving salt tolerance associated with metabolic balance, polyamine (PAs) accumulation, and Na+ transport in creeping bentgrass (Agrostis stolonifera). RESULTS:CTS pretreatment significantly alleviated declines in relative water content, photosynthesis, photochemical efficiency, and water use efficiency in leaves under salt stress. Exogenous CTS increased endogenous PAs accumulation, antioxidant enzyme (SOD, POD, and CAT) activities, and sucrose accumulation and metabolism through the activation of sucrose synthase and pyruvate kinase activities, and inhibition of invertase activity. The CTS also improved total amino acids, glutamic acid, and ?-aminobutyric acid (GABA) accumulation. In addition, CTS-pretreated plants exhibited significantly higher Na+ content in roots and lower Na+ accumulation in leaves then untreated plants in response to salt stress. However, CTS had no significant effects on K+/Na+ ratio. Importantly, CTS enhanced salt overly sensitive (SOS) pathways and also up-regulated the expression of AsHKT1 and genes (AsNHX4, AsNHX5, and AsNHX6) encoding Na+/H+ exchangers under salt stress. CONCLUSIONS:The application of CTS increased antioxidant enzyme activities, thereby reducing oxidative damage to roots and leaves. CTS-induced increases in sucrose and GABA accumulation and metabolism played important roles in osmotic adjustment and energy metabolism during salt stress. The CTS also enhanced SOS pathway associated with Na+ excretion from cytosol into rhizosphere, increased AsHKT1 expression inhibiting Na+ transport to the photosynthetic tissues, and also up-regulated the expression of AsNHX4, AsNHX5, and AsNHX6 promoting the capacity of Na+ compartmentalization in roots and leaves under salt stress. In addition, CTS-induced PAs accumulation could be an important regulatory mechanism contributing to enhanced salt tolerance. These findings reveal new functions of CTS on regulating Na+ transport, enhancing sugars and amino acids metabolism for osmotic adjustment and energy supply, and increasing PAs accumulation when creeping bentgrass responds to salt stress.
Project description:BACKGROUND: GABA (gamma-aminobutyric acid) is a non protein amino acid that has been reported to accumulate in a number of plant species when subjected to high salinity and many other environmental constraints. However, no experimental data are to date available on the molecular function of GABA and the involvement of its metabolism in salt stress tolerance in higher plants. Here, we investigated the regulation of GABA metabolism in Arabidopsis thaliana at the metabolite, enzymatic activity and gene transcription levels upon NaCl stress. RESULTS: We identified the GABA transaminase (GABA-T), the first step of GABA catabolism, as the most responsive to NaCl. We further performed a functional analysis of the corresponding gene POP2 and demonstrated that the previously isolated loss-of-function pop2-1 mutant was oversensitive to ionic stress but not to osmotic stress suggesting a specific role in salt tolerance. NaCl oversensitivity was not associated with overaccumulation of Na+ and Cl- but mutant showed a slight decrease in K+. To bring insights into POP2 function, a promoter-reporter gene strategy was used and showed that POP2 was mainly expressed in roots under control conditions and was induced in primary root apex and aerial parts of plants in response to NaCl. Additionally, GC-MS- and UPLC-based metabolite profiling revealed major changes in roots of pop2-1 mutant upon NaCl stress including accumulation of amino acids and decrease in carbohydrates content. CONCLUSIONS: GABA metabolism was overall up-regulated in response to NaCl in Arabidopsis. Particularly, GABA-T was found to play a pivotal function and impairment of this step was responsible for a decrease in salt tolerance indicating that GABA catabolism was a determinant of Arabidopsis salt tolerance. GABA-T would act in salt responses in linking N and C metabolisms in roots.
Project description:Salt stress is one of the main factors that affect both growth and development of plants. Maintaining K+/Na+ balance in the cytoplasm is important for metabolism as well as salt resistance in plants. In the present study, we monitored the growth (height and diameter) of transgenic Populus alba × P. berolinensis trees (ABJ01) carrying JERF36s gene (a tomato jasmonic/ethylene responsive factors gene) over 4 years, which showed faster growth and significant salt tolerance compared with non-transgenic poplar trees (9#). The expression of NHX1 and SOS1 genes that encode Na+/H+ antiporters in the vacuole and plasma membranes was measured in leaves under NaCl stress. Non-invasive micro-test techniques (NMT) were used to analyse ion flux of Na+, K+, and H+ in the root tip of seedlings under treatment with100 mM NaCl for 7, 15, and 30 days. Results showed that the expression of NHX1 and SOS1 was much higher in ABJ01 compared with 9#, and the Na+ efflux and H+ influx fluxes of root were remarkable higher in ABJ01 than in 9#, but K+ efflux exhibited lower level. All above suggest that salt stress induces NHX1 and SOS1 to a greater expression level in ABJ01, resulting in the accumulation of Na+/H+ antiporter to better maintain K+/Na+ balance in the cytoplasm of this enhanced salt resistant variety. This may help us to better understand the mechanism of transgenic poplars with improving salt tolerance by overexpressing JERF36s and could provide a basis for future breeding programs aimed at improving salt resistance in transgenic poplar.
Project description:One of the major abiotic stresses affecting agriculture is soil salinity, which reduces crop yield and, consequently, revenue for farmers. Although tomato is an important agricultural species, elite varieties are poor at withstanding salinity stress. Thus, a feasible way of improving yield under conditions of salinity stress is to breed for improved salt tolerance. In this study, we analysed the physiological and genetic parameters of 23 tomato accessions in order to identify possible traits to be used by plant breeders to develop more tolerant tomato varieties. Although we observed a wide range of Na(+) concentrations within the leaves, stems and roots, the maintenance of growth in the presence of 100 mM NaCl did not correlate with the exclusion or accumulation of Na(+). Nor could we correlate the growth with accumulation of sugars and proline or with the expression of any gene involved in the homoeostasis of Na(+) in the plant. However, several significant correlations between gene expression and Na(+) accumulation were observed. For instance, Na(+) concentrations both in the leaves and stems were positively correlated with HKT1;2 expression in the roots, and Na(+) concentration measured in the roots was positively correlated with HKT1;1 expression also in the roots. Higher and lower Na(+) accumulation in the roots and leaves were significantly correlated with higher NHX3 and NHX1 expression in the roots, respectively. These results suggest that, in tomato, for a particular level of tolerance to salinity, a complex relationship between Na(+) concentration in the cells and tissue tolerance defines the salinity tolerance of individual tomato accessions. In tomato it is likely that tissue and salinity tolerance work independently, making tolerance to salinity depend on their relative effects rather than on one of these mechanisms alone.
Project description:Melatonin (MT) is a multifunctional molecule in animals and plants and is involved in defense against salinity stress in various plant species. In this study, MT pretreatment was simultaneously applied to the roots and leaves of sweet potato seedlings [Ipomoea batatas (L.) Lam.], which is an important food and industry crop worldwide, followed by treatment of 150 mM NaCl. The roles of MT in mediating K+/Na+ homeostasis and lipid metabolism in salinized sweet potato were investigated. Exogenous MT enhanced the resistance to NaCl and improved K+/Na+ homeostasis in sweet potato seedlings as indicated by the low reduced K+ content in tissues and low accumulation of Na+ content in the shoot. Electrophysiological experiments revealed that exogenous MT significantly suppressed NaCl-induced K+ efflux in sweet potato roots and mesophyll tissues. Further experiments showed that MT enhanced the plasma membrane (PM) H+-ATPase activity and intracellular adenosine triphosphate (ATP) level in the roots and leaves of salinized sweet potato. Lipidomic profiling revealed that exogenous MT completely prevented salt-induced triacylglycerol (TAG) accumulation in the leaves. In addition, MT upregulated the expression of genes related to TAG breakdown, fatty acid (FA) ?-oxidation, and energy turnover. Chemical inhibition of the ?-oxidation pathway led to drastic accumulation of lipid droplets in the vegetative tissues of NaCl-stressed sweet potato and simultaneously disrupted the MT-stimulated energy state, PM H+-ATPase activity, and K+/Na+ homeostasis. Results revealed that exogenous MT stimulated TAG breakdown, FA ?-oxidation, and energy turnover under salinity conditions, thereby contributing to the maintenance of PM H+-ATPase activity and K+/Na+ homeostasis in sweet potato.
Project description:The non-protein amino acid ?-aminobutyric acid (GABA) rapidly accumulates in plant tissues in response to salinity. However, the physiological rationale for this elevation remains elusive. This study compared electrophysiological and whole-plant responses of salt-treated Arabidopsis mutants pop2-5 and gad1,2, which have different abilities to accumulate GABA. The pop2-5 mutant, which was able to overaccumulate GABA in its roots, showed a salt-tolerant phenotype. On the contrary, the gad1,2 mutant, lacking the ability to convert glutamate to GABA, showed oversensitivity to salinity. The greater salinity tolerance of the pop2-5 line was explained by: (i) the role of GABA in stress-induced activation of H+-ATPase, thus leading to better membrane potential maintenance and reduced stress-induced K+ leak from roots; (ii) reduced rates of net Na+ uptake; (iii) higher expression of SOS1 and NHX1 genes in the leaves, which contributed to reducing Na+ concentration in the cytoplasm by excluding Na+ to apoplast and sequestering Na+ in the vacuoles; (iv) a lower rate of H2O2 production and reduced reactive oxygen species-inducible K+ efflux from root epidermis; and (v) better K+ retention in the shoot associated with the lower expression level of GORK channels in plant leaves.
Project description:Salinity threatens productivity of economically important crops such as tomato (Solanum lycopersicum L.). WRKY transcription factors appear, from a growing body of knowledge, as important regulators of abiotic stresses tolerance. Tomato SlWRKY3 is a nuclear protein binding to the consensus CGTTGACC/T W box. SlWRKY3 is preferentially expressed in aged organs, and is rapidly induced by NaCl, KCl, and drought. In addition, SlWRKY3 responds to salicylic acid, and 35S::SlWRKY3 tomatoes showed under salt treatment reduced contents of salicylic acid. In tomato, overexpression of SlWRKY3 impacted multiple aspects of salinity tolerance. Indeed, salinized (125 mM NaCl, 20 days) 35S::SlWRKY3 tomato plants displayed reduced oxidative stress and proline contents compared to WT. Physiological parameters related to plant growth (shoot and root biomass) and photosynthesis (stomatal conductance and chlorophyll a content) were retained in transgenic plants, together with lower Na+ contents in leaves, and higher accumulation of K+ and Ca2+. Microarray analysis confirmed that many stress-related genes were already up-regulated in transgenic tomatoes under optimal conditions of growth, including genes coding for antioxidant enzymes, ion and water transporters, or plant defense proteins. Together, these results indicate that SlWRKY3 is an important regulator of salinity tolerance in tomato.