GABA enhances physio-biochemical metabolism and antioxidant capacity of germinated hulless barley under NaCl stress

Effect of GABA combined with ultrasound stress germination treatment on phenolic content and antioxidant activity of highland barley

BACKGROUND

This study investigated the effects of γ-aminobutyric acid (GABA) combined with ultrasonic stress germination (AUG) treatment on the phenolic content and antioxidant activity of highland barley (HB). Key variables, including germination times (ranging from 0 to 96 h), ultrasonic power (200-500 W), and GABA concentration (5-20 mmol/L), were optimized using response surface methodology (RSM) to enhance the enrichment of phenolic compounds. Furthermore, the study assessed the content, composition, and antioxidant activities of phenolic compounds in HB under various treatment conditions such as germination alone (G), ultrasonic stress germination (UG), and AUG treatment.

RESULTS

The study identified optimal conditions for the phenolic enrichment of HB, which included a germination time of 60 h, an ultrasound power of 300 W, and a GABA concentration of 15 mmol L-1. Under these conditions, the total phenolic content (TPC) in HB was measured at 7.73 milligrams of gallic acid equivalents per gram dry weight (mg GAE/g DW), representing a 34.96% enhancement compared to untreated HB. Notably, all treatment modalities - G, UG, and AUG - significantly increased the phenolic content and antioxidant activity in HB, with the AUG treatment proving to be the most effective.

CONCLUSION

These obtained results suggest that AUG treatment is a promising processing method for enriching phenolic compounds and improving antioxidant activity in HB. Subsequently, the AUG-treated HB can be used to develop phenolic-rich germinated functional foods to further broaden the application of HB. © 2024 Society of Chemical Industry.

Gamma-aminobutyric acid (GABA) improves salinity stress tolerance in soybean seedlings by modulating their mineral nutrition, osmolyte contents, and ascorbate-glutathione cycle

BACKGROUND

In plants, GABA plays a critical role in regulating salinity stress tolerance. However, the response of soybean seedlings (Glycine max L.) to exogenous gamma-aminobutyric acid (GABA) under saline stress conditions has not been fully elucidated.

RESULTS

This study investigated the effects of exogenous GABA (2 mM) on plant biomass and the physiological mechanism through which soybean plants are affected by saline stress conditions (0, 40, and 80 mM of NaCl and Na2SO4 at a 1:1 molar ratio). We noticed that increased salinity stress negatively impacted the growth and metabolism of soybean seedlings, compared to control. The root-stem-leaf biomass (27- and 33%, 20- and 58%, and 25- and 59% under 40- and 80 mM stress, respectively]) and the concentration of chlorophyll a and chlorophyll b significantly decreased. Moreover, the carotenoid content increased significantly (by 35%) following treatment with 40 mM stress. The results exhibited significant increase in the concentration of hydrogen peroxide (H2O2), malondialdehyde (MDA), dehydroascorbic acid (DHA) oxidized glutathione (GSSG), Na+, and Cl- under 40- and 80 mM stress levels, respectively. However, the concentration of mineral nutrients, soluble proteins, and soluble sugars reduced significantly under both salinity stress levels. In contrast, the proline and glycine betaine concentrations increased compared with those in the control group. Moreover, the enzymatic activities of ascorbate peroxidase, monodehydroascorbate reductase, glutathione reductase, and glutathione peroxidase decreased significantly, while those of superoxide dismutase, catalase, peroxidase, and dehydroascorbate reductase increased following saline stress, indicating the overall sensitivity of the ascorbate-glutathione cycle (AsA-GSH). However, exogenous GABA decreased Na+, Cl-, H2O2, and MDA concentration but enhanced photosynthetic pigments, mineral nutrients (K+, K+/Na+ ratio, Zn2+, Fe2+, Mg2+, and Ca2+); osmolytes (proline, glycine betaine, soluble sugar, and soluble protein); enzymatic antioxidant activities; and AsA-GSH pools, thus reducing salinity-associated stress damage and resulting in improved growth and biomass. The positive impact of exogenously applied GABA on soybean plants could be attributed to its ability to improve their physiological stress response mechanisms and reduce harmful substances.

CONCLUSION

Applying GABA to soybean plants could be an effective strategy for mitigating salinity stress. In the future, molecular studies may contribute to a better understanding of the mechanisms by which GABA regulates salt tolerance in soybeans.

Low-temperature acclimation related with developmental regulations of polyamines and ethylene metabolism in wheat recombinant inbred lines

Winter survival is determined by complicated developmental regulations enabling wheat to adjust their transcriptome and metabolome to develop low temperature (LT) tolerance. The aim of the study was to clarify the metabolic responses developmentally regulated in six F6 recombinant inbred lines from a cross between Pishtaz (spring parent) and Mironovskaya 808 (winter parent). Spring genotypes, including pishtaz, RILs 4006 and 4014 showed lower LT tolerance, PAs (except the spermin), GABA and proline contents and DPPH• scavenging capacity. In these genotypes, genes and enzymes involved in the pathways of PAs and GABA degradation and ethylene biosynthesis were more active than other genotypes. RILs 4012 and 4016 with short vernalization displayed higher tolerance and lower H2O2 content compared to Pishtaz. Strong vernalization requirements in winter and facultative genotypes (Mironovskaya 808 parent and RILs 4003 and 4005) results in up-regulation of the metabolites and genes involved in PAs and GABA biosynthesis pathways (particularly when vernalization fulfillment occurred) to establish high tolerance as compared to genotypes without vernalization requirement. LT tolerance in all genotypes significantly decreased after vernalization fulfillment in February. Results indicated that LT tolerance was partly validated from developmental regulation of PAs, GABA, and ethylene metabolism during venalization and LT acclimation.

Salicylic Acid and α-Tocopherol Ameliorate Salinity Impact on Wheat

Background: Soil salinity negatively impacts agricultural productivity. Consequently, strategies should be developed to inculcate a salinity tolerance in crops for sustainable food production. Growth regulators play a vital role in regulating salinity stress tolerance. Methods: Thus, we examined the effect of exogenous salicylic acid (SA) and alpha-tocopherol (TP) (100 mg/L) on the morphophysio-biochemical responses of two wheat cultivars (Pirsabak-15 and Shankar) to salinity stress (0 and 40 mM). Results: Both Pirsabak-15 and Shankar cultivars were negatively affected by salinity stress. For instance, salinity reduced growth attributes (i.e., leaf fresh and dry weight, leaf moisture content, leaf area ratio, shoot and root dry weight, shoot and root length, as well as root-shoot ratio), pigments (chlorophyll a, chlorophyll a, and carotenoids) but increased hydrogen peroxide (H₂O₂), malondialdehyde (MDA), and endogenous TP in both cultivars. Among the antioxidant enzymes, salinity enhanced the activity of peroxidase (POD) and polyphenol oxidase (PPO) in Pirsabak-15; glutathione reductase (GR) and PPO in Shankar, while ascorbate peroxidase (APOX) was present in both cultivars. SA and TP could improve the salinity tolerance by improving growth and photosynthetic pigments and reducing MDA and H₂O₂. In general, the exogenous application did not have a positive effect on antioxidant enzymes; however, it increased PPO in Pirsabak-15 and SOD in the Shankar cultivar. Conclusions: Consequently, we suggest that SA and TP could have enhanced the salinity tolerance of our selected wheat cultivars by modulating their physiological mechanisms in a manner that resulted in improved growth. Future molecular studies can contribute to a better understanding of the mechanisms by which SA and TP regulate the selected wheat cultivars underlying salinity tolerance mechanisms.

Exogenous γ-aminobutyric acid (GABA) mitigated salinity-induced impairments in mungbean plants by regulating their nitrogen metabolism and antioxidant potential

BACKGROUND

Increasing soil salinization has a detrimental effect on agricultural productivity.Therefore, strategies are needed to induce salinity-tolerance in crop species for sustainable foodproduction. γ-aminobutyric acid (GABA) plays a key role in regulating plant salinity stresstolerance. However, it remains largely unknown how mungbean plants (Vigna radiata L.) respondto exogenous GABA under salinity stress.

METHODS

Thus, we evaluated the effect of exogenous GABA (1.5 mM) on the growth and physiobiochemicalresponse mechanism of mungbean plants to saline stress (0-, 50-, and 100 mM [NaCland Na2SO4, at a 1:1 molar ratio]).

RESULTS

Increased saline stress adversely affected mungbean plants' growth and metabolism. Forinstance, leaf-stem-root biomass (34- and 56%, 31- and 53%, and 27- and 56% under 50- and 100mM, respectively]) and chlorophyll concentrations declined. The carotenoid level increased (10%)at 50 mM and remained unaffected at 100 mM. Hydrogen peroxide (H2O2), malondialdehyde(MDA), osmolytes (soluble sugars, soluble proteins, proline), total phenolic content, andenzymatic activities of superoxide dismutase (SOD), ascorbate peroxidase (APX), peroxidase(POD), glutathione reductase (GTR), and polyphenol oxidation (PPO) were significantlyincreased. In leaves, salinity caused a significant increase in Na+ concentration but a decrease inK+ concentration, resulting in a low K+/Na+ concentration (51- and 71% under 50- and 100- mMstress). Additionally, nitrogen concentration and the activities of nitrate reductase (NR) andglutamine synthetase (GS) decreased significantly. The reduction in glutamate synthase (GOGAT)activity was only significant (65%) at 100 mM stress. Exogenous GABA decreased Na+, H2O2,and MDA concentrations but enhanced photosynthetic pigments, K+ and K+/Na+ ratio, Nmetabolism, osmolytes, and enzymatic antioxidant activities, thus reducing salinity-associatedstress damages, resulting in improved growth and biomass.

CONCLUSION

Exogenous GABA may have improved the salinity tolerance of mungbean plants by maintaining their morpho-physiological responses and reducing the accumulation of harmfulsubstances under salinity. Future molecular studies can contribute to a better understanding of themolecular mechanisms by which GABA regulates mungbean salinity tolerance.

Nutrient Composition of Germinated Foxtail Millet Flour Treated with Mixed Salt Solution and Slightly Acidic Electrolyzed Water

Germination of millet can improve its consumption quality, optimize its nutritional composition, and promote the accumulation of functional components such as γ-aminobutyric acid (GABA). In the present study, foxtail millet was germinated with tap water, a mixed salt solution of 7.5 mmol/L NaCl and 15 mmol/L CaCl₂, and slightly acidic electrolyzed water (SAEW) with three available chlorine concentrations (ACCs; 10.92, 20.25, and 30.35 mg/L). The effects of the salt solution and SAEW on the germination of foxtail millet and the GABA, crude protein, and amino acid composition of the germinated millet flour were analyzed. The results showed that the salt solution and SAEW treatments promoted the growth of millet sprouts, contributed to the accumulation of GABA in germinated millet flour, and optimized the protein and amino acid composition. The GABA content of germinated foxtail millet flour treated with salt solution for 60 h (336.52 mg/100 g) was 29.5 times higher than that of ungerminated millet flour. In conclusion, the highest GABA content and amino acid scores of germinated millet flour obtained by germination treatment with salt solution at 25 °C and 86% humidity for 60 h were more acceptable for human nutritional requirements.

Exogenous GABA improves the resistance of apple seedlings to long-term drought stress by enhancing GABA shunt and secondary cell wall biosynthesis

Drought stress is an important factor limiting apple production. γ-Aminobutyric acid (GABA) exists widely in plants and participates in the response to abiotic stress as a metabolite or signaling molecule. The role of exogenous GABA in apple plants, response to long-term drought stress remains unclear. Our study confirmed that exogenous GABA affects the drought resistance of apple plants under long-term drought stress. We found that 1 mM exogenous GABA improved the resistance of apple seedlings to long-term drought stress. The plants showed better growth, less reactive oxygen radical accumulation, less damage to cell membranes and greater active photosynthetic capacity. Under long-term drought stress, exogenous GABA facilitated GABA shunt, resulting in more accumulation of organic acids, namely citric acid, succinic acid and malic acid, in roots and stems of apple seedlings. In addition, exogenous GABA upregulated the expression of cellulose-related genes and lignin-related genes, and activated secondary cell wall-related transcription factors to synthesize more cellulose and lignin. A multiple factorial analysis confirmed that the GABA shunt and the biosynthesis of cellulose and lignin substantially contributed to the growth of apple seedlings with the application of exogenous GABA under long-term drought stress. Our results suggested that exogenous GABA improved the resistance of apple seedlings to long-term drought stress by enhancing GABA shunt and secondary cell wall biosynthesis.

Nitric oxide mediates melatonin-induced isoflavone accumulation and growth improvement in germinating soybeans under NaCl stress

The involvement of nitric oxide (NO) in exogenous melatonin (MT)-induced isoflavone accumulation and growth improvement in NaCl-stressed soybeans was investigated in this study. The results demonstrated that MT increased the activity of nitrate reductase (NR) and upregulated the relative expression of NR1, NR2, and nitric oxide synthase1, which subsequently led to an increase in NO content. MT and sodium nitroprusside (SNP, as an NO donor) markedly increased isoflavone content by enhancing the activities of cinnamic acid 4-hydroxylase (C4H) and phenylalanine ammonia lyase (PAL), and by upregulating gene expression of C4H, Isoflavone synthase, PAL, and Chalcone isomerase 1A, which are involved in isoflavone biosynthesis. Moreover, MT, as well as SNP, improved the growth and biomass of NaCl-treated soybeans by increasing the activities of superoxide dismutase, catalase, and peroxidase, and reducing the accumulation of H₂O₂ and O₂^•- in soybeans under NaCl stress. These MT-induced responses were entirely reversed by the supply of 4-carboxyphenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (cPTIO, a specific scavenger of NO), which in turn considerably decreased endogenous NO content. These results suggest that NO acts as an important downstream signal molecule, mediating MT-induced isoflavone accumulation and growth improvement in NaCl-stressed soybeans.

Extensive cross-talk among stress-regulated protective metabolites, biogenic-amines and phytohormone-signalling, co-ordinated by dopamine-mediated seed-priming, governs tolerance against fluoride stress in rice

Seed priming with dopamine reduced fluoride bioaccumulation, induced endogenous dopamine level, thereby orchestrating phytohormone homeostasis and biogenic amine metabolism, and modulating osmolyte and antioxidant machinery to enhance fluoride tolerance in rice. The aim of this study was to decipher the efficacy of seed priming with dopamine in curtailing the adverse impacts of fluoride toxicity in rice seedlings. Fluoride-stressed seedlings exhibited severe growth retardation, high fluoride bioaccumulation, electrolyte leakage and marked cellular injuries. Dopamine priming stimulated the overall physiological growth parameters during stress, via reduced formation of H₂O₂, malondialdehyde and methylglyoxal, due to lesser fluoride-accumulation. Fluoride stress-induced endogenous dopamine level was further induced upon dopamine priming, marked by the up regulated DOPA decarboxylase expression. Additionally, dopamine treatment led to escalated activity of catalase, superoxide dismutase and glutathione peroxidase in the stressed seedlings, concomitant with altered CAT, SOD and GPX expression. The higher accumulation of protective osmolytes (proline and total amino acids) and non-enzymatic antioxidants (phenolics, flavonoids, anthocyanins, glutathione and carotenoids), upon dopamine priming, during fluoride stress, could be linked with the altered expression pattern of the respective genes. Dopamine promoted active utilization of the biogenic amine (polyamines and ϒ-amino butyric acid) pools for toxicity mitigation, correlated with the modulation of the concerned enzyme activity and gene expression. Dopamine stimulated the accumulation of phytohormones like gibberellin and salicylic acid, via inducing the biosynthetic genes like gibberellin-3-oxidase (GA3ox) and isochorismate synthase (ICS), respectively, while depreciating the abscisic acid and melatonin level during fluoride stress. To our knowledge, this is the first documented report for the remedial role of dopamine priming against fluoride stress in any plant species. This study will open new arenas in sustainable agriculture for the exploitation of this pulsating biomolecule against fluoride stress.

Exogenous γ-Aminobutyric Acid (GABA) Application Mitigates Salinity Stress in Maize Plants

The effect of γ-Aminobutyrate (GABA) on maize seedlings under saline stress conditions has not been well tested in previous literature. Maize seedlings were subjected to two saline water concentrations (50 and 100 mM NaCl), with distilled water as the control. Maize seedlings under saline and control conditions were sprayed with GABA at two concentrations (0.5 and 1 mM). Our results indicated that GABA application (1 mM) significantly enhanced plant growth parameters (fresh shoots and fresh roots by 80.43% and 47.13%, respectively) and leaf pigments (chlorophyll a, b, and total chlorophyll by 22.88%, 56.80%, and 36.21%, respectively) compared to untreated seedlings under the highest saline level. Additionally, under 100 mM NaCl, methylglyoxal (MG), malondialdehyde (MDA), and hydrogen peroxidase (H₂O₂) were reduced by 1 mM GABA application by 43.66%, 33.40%, and 35.98%, respectively. Moreover, maize seedlings that were treated with 1 mM GABA contained a lower Na content (22.04%) and a higher K content (60.06%), compared to the control under 100 mM NaCl. Peroxidase, catalase, ascorbate peroxidase, and superoxide dismutase activities were improved (24.62%, 15.98%, 62.13%, and 70.07%, respectively) by the highest GABA rate, under the highest stress level. Seedlings treated with GABA under saline conditions showed higher levels of expression of the potassium transporter protein (ZmHKT1) gene, and lower expression of the ZmSOS1 and ZmNHX1 genes, compared to untreated seedlings. In conclusion, GABA application as a foliar treatment could be a promising strategy to mitigate salinity stress in maize plants.

Antifungal Peptide P852 Controls Fusarium Wilt in Faba Bean (Viciafaba L.) by Promoting Antioxidant Defense and Isoquinoline Alkaloid, Betaine, and Arginine Biosyntheses

Green pesticides are highly desirable, as they are environmentally friendly and efficient. In this study, the antifungal peptide P852 was employed to suppress Fusarium wilt in the Faba bean. The disease index and a range of physiological and metabolomic analyses were performed to explore the interactions between P852 and the fungal disease. The incidence and disease index of Fusarium wilt were substantially decreased in diseased Faba beans that were treated with two different concentrations of P852 in both the climate chamber and field trial. For the first time, P852 exhibited potent antifungal effects on Fusarium in an open field condition. To explore the mechanisms that underlie P852′s antifungal effects, P852 treatment was found to significantly enhance antioxidant enzyme capacities including guaiacol peroxidase (POD), superoxide dismutase (SOD), catalase (CAT), and the activities of antifungal enzymes including chitinase and β-1,3-glucanase, as well as plant dry and fresh weights, and chlorophyll content compared to the control group (p ≤ 0.05). Metabolomics analysis of the diseased Faba bean treated with P852 showed changes in the TCA cycle, biological pathways, and many primary and secondary metabolites. The Faba bean treated with a low concentration of P852 (1 μg/mL, IC₅₀) led to upregulated arginine and isoquinoline alkaloid biosynthesis, whereas those treated with a high concentration of P852 (10 μg/mL, MFC) exhibited enhanced betaine and arginine accumulation. Taken together, these findings suggest that P852 induces plant tolerance under Fusarium attack by enhancing the activities of antioxidant and antifungal enzymes, and restoring plant growth and development.

The effect of Azorhizobium caulinodans ORS571 and γ-aminobutyric acid on salt tolerance of Sesbania rostrata

Salt stress seriously affects plant growth and crop yield, and has become an important factor that threatens the soil quality worldwide. In recent years, the cultivation of salt-tolerant plants such as Sesbania rostrata has a positive effect on improving coastal saline-alkali land. Microbial inoculation and GABA addition have been shown to enhance the plant tolerance in response to the abiotic stresses, but studies in green manure crops and the revelation of related mechanisms are not clear. In this study, the effects of inoculation with Azorhizobium caulinodans ORS571 and exogenous addition of γ-Aminobutyric Acid (GABA; 200 mg·L^-1) on the growth and development of S. rostrata under salt stress were investigated using potting experiments of vermiculite. The results showed that inoculation with ORS571 significantly increased the plant height, biomass, chlorophyll content, proline content (PRO), catalase (CAT) activity, and superoxide dismutase (SOD) activity of S. rostrata and reduced the malondialdehyde (MDA) level of leaves. The exogenous addition of GABA also increased the height, biomass, and CAT activity and reduced the MDA and PRO level of leaves. In addition, exogenous addition of GABA still had a certain improvement on the CAT activity and chlorophyll content of the ORS571-S. rostrata symbiotic system. In conclusion, ORS571 inoculation and GABA application have a positive effect on improving the salt stress tolerance in S. rostrata, which are closely associated with increasing chlorophyll synthesis and antioxidant enzyme activity and changing the amino acid content. Therefore, it can be used as a potential biological measure to improve the saline-alkali land.

Synthesis of γ-Aminobutyric Acid-Modified Chitooligosaccharide Derivative and Enhancing Salt Resistance of Wheat Seedlings

Salinity is one of the major abiotic stresses limiting crop growth and productivity worldwide. Salt stress during germination degenerates crop establishment and declines yield in wheat, therefore alleviating the damage of salt stress to wheat seedlings is crucial. Chitooligosaccharide (COS) was grafted with γ-aminobutyric acid based on the idea of bioactive molecular splicing, and the differences in salt resistance before and after grafting were compared. The expected derivative was successfully synthesized and exhibited better salt resistance-inducing activity than the raw materials. By activating antioxidant enzymes such as superoxide dismutases (SOD), catalase (CAT) and phenylalanine ammonia-lyase (PAL) and subsequently eliminating reactive oxygen species (ROS) in a timely manner, the rate of O⁻₂ production and H₂O₂ content of wheat seedlings were reduced, and the dynamic balance of free radical metabolism in the plant body was maintained. A significantly reduced MDA content, reduced relative permeability of the cell membrane, and decreased degree of damage to the cell membrane were observed. A significant increase in the content of soluble sugar, maintenance of osmotic regulation and the stability of the cell membrane structure, effective reduction in the salt stress-induced damage to wheat, and the induction of wheat seedling growth were also observed, thereby improving the salt tolerance of wheat seedlings.

Enhanced total flavonoid accumulation and alleviated growth inhibition of germinating soybeans by GABA under UV-B stress

Germination of soybeans under ultraviolet-B (UV-B) treatment is a simple and effective way to enrich soybean isoflavones, but its mechanism of action is not yet clear. G-Aminobutyric acid (GABA) is a signaling molecule that is involved in the accumulation of secondary metabolites as well as the regulation of plant development and metabolism. In this study, the effects of exogenous GABA and its inhibitors on the physiological and biochemical, antioxidant systems, total flavonoid content, activity and gene expression of isoflavone metabolism related enzyme in germinating soybeans under UV-B treatment were investigated. Compared to UV-B treatment alone, soybean treated with GABA (5 mM) in combination with UV-B significantly increased sprout length, fresh weight, Ca²⁺ inward flow and peroxidase and catalase activities, and decreased malondialdehyde and H₂O₂ and O₂˙⁻ fluorescence intensity, while soybean treated with GABA inhibitor showed the opposite trend. Meanwhile, total flavonoid content increased by 11.2% and 6.7%, respectively, in 2- and 4 day-old soybeans under UV-B treatment, compared to UV-B treatment alone. Moreover, the application of GABA under UV treatment significantly increased the activity of phenylalanine ammonia-lyase and cinnamic acid-4-hydroxylase, with values increasing by 43.6% and 18.5%, respectively, in four-day-old soybean compared to UV treatment alone, which also increased the relative expression of key genes involved in isoflavone metabolism. The GABA inhibitor 3-mercaptopropionic acid blocked these occurrences. According to this research, GABA could operate as a signaling molecule to mediate isoflavone accumulation in soybean sprouts under UV radiation and stimulate soybean sprout growth.

Effect of GABA on isoflavone metabolism in soybeans under UV-B treatment.

Activation of the ABA Signal Pathway Mediated by GABA Improves the Drought Resistance of Apple Seedlings

Drought seriously affects the yield and quality of apples. γ-aminobutyric acid (GABA) plays an important role in the responses of plants to various stresses. However, the role and possible mechanism of GABA in the drought response of apple seedlings remain unknown. To explore the effect of GABA on apple seedlings under drought stress, seedlings of Malus hupehensis were treated with seven concentrations of GABA, and the response of seedlings under 15-day drought stress was observed. The results showed that 0.5 mM GABA was the most effective at relieving drought stress. Treatment with GABA reduced the relative electrical conductivity and MDA content of leaves induced by drought stress and significantly increased the relative water content of leaves. Exogenous GABA significantly decreased the stomatal conductance and intercellular carbon dioxide concentration and transpiration rate, and it significantly increased the photosynthetic rate under drought. GABA also reduced the accumulation of superoxide anions and hydrogen peroxide in leaf tissues under drought and increased the activities of POD, SOD, and CAT and the content of GABA. Exogenous treatment with GABA acted through the accumulation of abscisic acid (ABA) in the leaves to significantly decrease stomatal conductance and increase the stomatal closure rate, and the levels of expression of ABA-related genes PYL4, ABI1, ABI2, HAB1, ABF3, and OST1 changed in response to drought. Taken together, exogenous GABA can enhance the drought tolerance of apple seedlings.

Effect of γ-aminobutyric Acid on Phenolics Metabolism in Barley Seedlings under Low NaCl Treatment

It has been revealed that high NaCl stress (>60 mmol L^-1) induced phenolics accumulation in barley seedlings, with γ-aminobutyric acid (GABA) playing a key role. Interestingly, low NaCl stimulus (20 mmol L^-1) enhancing phenolics synthesis and growth of barley seedlings was also reported recently. Hence, exogenous GABA and its bio-synthesis inhibitor 3-mercaptopropionic acid (3-MP) were applied to reveal the mechanism of GABA regulating phenolics metabolism in barley seedlings treated with 20 mmol L^-1 NaCl. The contents of total phenolics and flavonoids significantly increased by 11.64% and 14.52% under NaCl, respectively. The addition of GABA further increased phenolics and flavonoids contents, especially for gallic acid, protocatechuic acid, caffeic acid, and quercetin, compared with NaCl treatment. Simultaneously, GABA increased the activities and mRNA levels of phenylalanine ammonia lyase (PAL), cinnamic acid 4-hydroxylase (C4H), and 4-coumalyl CoA ligase (4CL). The addition of 3-MP suppressed the above effects, except for increasing the protein levels of PAL, C4H, and 4CL. Low concentration of NaCl not only promoted growth, but also stimulated endogenous GABA metabolism to affect key enzymes activities and mRNA levels for phenolics synthesis in barley seedlings.

Potassium-enriched clinoptilolite zeolite mitigates the adverse impacts of salinity stress in perennial ryegrass (Lolium perenne L.) by increasing silicon absorption and improving the K/Na ratio

Salinity is a major abiotic stress that adversely affects turfgrass growth. Clinoptilolite zeolite, a silicon (Si)-rich mineral, may allow these plants to cope with salinity. Therefore, in the present study, the effects of ordinary clinoptilolite zeolite (OZ) and potassium-enriched clinoptilolite zeolite (K-EZ) on the growth of perennial ryegrass (Lolium perenne L.) were assessed under salinity stress. Perennial ryegrass seeds were cultured in soil mixtures amended, or not, with OZ or K-EZ, then exposed to three salinity levels (0, 50 or 100 mM NaCl) for three months. Control plants were grown in the same soil mixture without zeolites, but not exposed to salinity. In salinity, the application of both types of zeolite significantly decreased Na content by 44.36% and 21.31%, but increased K content by 272.34% and 81.59%, as well as the K/Na ratio by 590.47% and 129.43%, in shoots and roots, respectively, compared to the no-zeolite treatment. Similarly, Si content in shoots increased by 28.33%. Amending the soil mixture with zeolite, especially K-EZ, enhanced relative water content, membrane stability index, total chlorophyll content, total soluble proteins, peroxidase and superoxide dismutase activities but reduced the contents of total soluble carbohydrates, hydrogen peroxide, and malondialdehyde in saline conditions. Shoot and root dry weight, root volume and root/shoot ratio also improved. Soil amendment with both forms of zeolite, as a Si-rich mineral, partially offset the negative impacts of salinity on perennial ryegrass, although K-EZ had more noticeable positive and beneficial effects. The amendment of growth media with zeolite may be an effective sustainable management practice for turfgrass used in landscaping and sports fields exposed to saline water.

The synergistic effect of traditional Chinese medicine prescription and rumen-protected γ-aminobutyric acid on beef cattle under heat stress

Traditional Chinese medicine (TCM) prescription or rumen-protected GABA (RP-GABA) can effectively relieve the heat stress (HS) in cattle, but the joint effects of TCM and RP-GABA on HS in beef cattle are not fully clarified. To investigate the effects of TCM or/and RP-GABA on growth performance, antioxidant capacity, serum parameters and heat shock proteins (HSPs) expression in beef cattle under HS ambient. A total of 40 Jinjiang yellow cattle were randomly divided into four groups: (a) control group (basal diet, BD), (b) TCM group (BD+TCM), (c) GABA group (BD+RP-GABA) and (d) TCM+GABA group (BD+TCM plus RP-GABA). Results indicated that the average daily feed intake (ADFI) was significantly elevated in the TCM+GABA group (p < 0.05), whereas, average daily gain (ADG) was elevated (p < 0.05) in the group of TCM (38.5%), GABA (35.4%) and TCM+GABA (41.5%) compared with the control group. Meanwhile, TCM+GABA exhibited prominently more positive effects in terms of SOD, BUN, T-CHO, TG, HDL-C and HSP70 (p < 0.05 or p < 0.01) than the control and other treatment groups. Therefore, TCM or GABA can effectively moderate the HS response in beef cattle by ameliorating antioxidant capacity, serum parameters and HSPs expression, meanwhile, the combination of them exerts a synergistic effect on HS alleviation.

Exogenous melatonin improves growth in hulless barley seedlings under cold stress by influencing the expression rhythms of circadian clock genes

Background

Melatonin is a hormone substance that exists in various living organisms. Since it was discovered in the pineal gland of cattle in 1956, the function of melatonin in animals has been roughly clarified. Nevertheless, in plants, the research on melatonin is still insufficient. Hulless barley (Hordeum vulgare L. var. nudum hook. f.) is a crop that originates from cultivated barley in the east, usually grown on the Qinghai-Tibet Plateau, becoming the most important food crop in this area. Although the genome and transcriptome research of highland barley has gradually increased recently years, there are still many problems about how hulless barley adapts to the cold climate of the Qinghai-Tibet Plateau.

Methods

In this study, we set three temperature conditions 25°C, 15°C, 5°C hulless barley seedlings, and at the same time soaked the hulless barley seeds with a 1 µM melatonin solution for 12 hours before the hulless barley seeds germinated. Afterwards, the growth and physiological indicators of hulless barley seedlings under different treatment conditions were determined. Meanwhile, the qRT-PCR method was used to determine the transcription level of the hulless barley circadian clock genes under different treatment conditions under continuous light conditions.

Results

The results showed the possible mechanism by which melatonin pretreatment can promote the growth of hulless barley under cold stress conditions by studying the effect of melatonin on the rhythm of the circadian clock system and some physiological indicators. The results revealed that the application of 1 µM melatonin could alleviate the growth inhibition of hulless barley seedlings caused by cold stress. In addition, exogenous melatonin could also restore the circadian rhythmic oscillation of circadian clock genes, such as HvCCA1 and HvTOC1, whose circadian rhythmic phenotypes were lost due to environmental cold stress. Additionally, the results confirmed that exogenous melatonin even reduced the accumulation of key physiological indicators under cold stress, including malondialdehyde and soluble sugars.

Discussion

Overall, these findings revealed an important mechanism that exogenous melatonin alleviated the inhibition of plant vegetative growths either by restoring the disrupted circadian rhythmic expression oscillations of clock genes, or by regulating the accumulation profiles of pivotal physiological indicators under cold stress.

Cross-talk between gama-aminobutyric acid and calcium ion regulates lipid biosynthesis in Monoraphidium sp. QLY-1 in response to combined treatment of fulvic acid and salinity stress

In this study, the cross-talk between gama-aminobutyric acid (GABA) and calcium ion (Ca²⁺) signalling in the regulation of lipid production and cell growth in microalgae under fulvic acid and salinity stress (FA-salinity treatment) was investigated. GABA enhanced the lipid content and lipid productivity rate considerably, which were 1.27 and 1.29 times higher than those of the control, respectively. The levels of biosynthetic gene transcription, GSH, Ca²⁺ and cellular GABA were promoted by GABA addition, but decreased the ROS levels. Furthermore, the application of Ca²⁺ also increased lipid synthesis by regulating ROS and GABA signalling and lipogenesis-related genes. These results indicated that cytosolic GABA and Ca²⁺ levels exert crucial cross-talk in the modulation of cell growth and lipid accumulation induced by FA-salinity treatment. Collectively, this study demonstrated the beneficial effects caused by induction of the combination of chemical compounds on lipid production and provided new insights into lipid synthesis in microalgae.

Gamma-aminobutyric acid (GABA) alleviates salt damage in tomato by modulating Na+ uptake, the GAD gene, amino acid synthesis and reactive oxygen species metabolism

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.

GORK Channel: A Master Switch of Plant Metabolism?

Potassium regulates a plethora of metabolic and developmental response in plants, and upon exposure to biotic and abiotic stresses a substantial K⁺ loss occurs from plant cells. The outward-rectifying potassium efflux GORK channels are central to this stress-induced K⁺ loss from the cytosol. In the mammalian systems, signaling molecules such as gamma-aminobutyric acid, G-proteins, ATP, inositol, and protein phosphatases were shown to operate as ligands controlling many K⁺ efflux channels. Here we present the evidence that the same molecules may also regulate GORK channels in plants. This mechanism enables operation of the GORK channels as a master switch of the cell metabolism, thus adjusting intracellular K⁺ homeostasis to altered environmental conditions, to maximize plant adaptive potential.

GABA-Alleviated Oxidative Injury Induced by Salinity, Osmotic Stress and their Combination by Regulating Cellular and Molecular Signals in Rice

This study was conducted in order to determine the effect of priming with γ-aminobutyric acid (GABA) at 0.5 mM on rice (Oryza sativa L.) seed germination under osmotic stress (OS) induced by polyethylene glycol (30 g/L PEG 6000); and salinity stress (S, 150 mM NaCl) and their combination (OS+S). Priming with GABA significantly alleviated the detrimental effects of OS, S and OS+S on seed germination and seedling growth. The photosynthetic system and water relation parameters were improved by GABA under stress. Priming treatment significantly increased the GABA content, sugars, protein, starch and glutathione reductase. GABA priming significantly reduced Na⁺ concentrations, proline, free radical and malonaldehyde and also significantly increased K⁺ concentration under the stress condition. Additionally, the activities of antioxidant enzymes, phenolic metabolism-related enzymes, detoxification-related enzymes and their transcription levels were improved by GABA priming under stress. In the GABA primed-plants, salinity stress alone resulted in an obvious increase in the expression level of Calcineurin B-like Protein-interacting protein Kinases (CIPKs) genes such as OsCIPK01, OsCIPK03, OsCIPK08 and OsCIPK15, and osmotic stress alone resulted in obvious increase in the expression of OsCIPK02, OsCIPK07 and OsCIPK09; and OS+S resulted in a significant up-regulation of OsCIPK12 and OsCIPK17. The results showed that salinity, osmotic stresses and their combination induced changes in cell ultra-morphology and cell cycle progression resulting in prolonged cell cycle development duration and inhibitory effects on rice seedlings growth. Hence, our findings suggested that the high tolerance to OS+S is closely associated with the capability of GABA priming to control the reactive oxygen species (ROS) level by inducing antioxidant enzymes, secondary metabolism and their transcription level. This knowledge provides new evidence for better understanding molecular mechanisms of GABA-regulating salinity and osmotic-combined stress tolerance during rice seed germination and development.

Physiological and metabolomics analyses of young and old leaves from wild and cultivated soybean seedlings under low-nitrogen conditions

BACKGROUND

It is critical to study the low nitrogen tolerance in wild soybean with extensive genetic diversity for improving cultivated soybean nitrogen use efficiency. Focusing on plant young and old leaves could provide new insights to low nitrogen tolerance research. This study compared the low nitrogen group with the control group on physiological and metabolomics changes in young and old leaves, respectively, then analyzed and compared the differences of these changes between cultivated and wild soybean. This study aimed to provide a theoretical basis for the molecular mechanism of soybean low nitrogen stress tolerance.

RESULTS

Wild soybean was less affected by low-nitrogen stress than cultivated soybean as assessed by plant biomass paraments, total carbon content and total nitrogen content. Gas-exchange coefficients and chlorophylls contents maintained relatively stable in wild soybean young leaves, but opposite in cultivated soybean. Wild soybean young leaves also increased the transport of beneficial ions, such as B3+, Fe3+, Mn2+, H2PO4- and C2O42-. In wild soybean old leaves, the nitrogen metabolism pathway was significant enhanced, especially the aspartic acid and GABA metabolisms. While in cultivated soybean, the nitrogen metabolism decreased obviously in young leaves but had no significant change in old leaves. The phenylpropanoid metabolism pathway was also activated in wild soybean. Contrary to cultivated soybeans, wild soybean tricarboxylic acid cycle and carbon metabolism including polyols and organic acids consolidated in old leaves and maintained a relative normal state in young leaves. These strategies could improve the antioxidant and N-fixation capacity in wild soybean.

CONCLUSION

The survival and growth of wild soybean under low nitrogen stress conditions relied on physiological adjustments and metabolic changes that occurred at the cellular level. Compared with cultivated soybean, wild soybean young leaves could maintain a relatively normal growth mainly owing to a significant enhancement of key amino acids and nonprotein nitrogen metabolism in old leaves, especially aspartic acid, proline metabolism which provided basis for nitrogen reutilization from old leaves to young leaves. Consolidating the tricarboxylic acid cycle, intensifying phenylpropanoid metabolism, and accumulating more polyols and organic acids also had positive effect on it.

Effect of Benzothiadiazole on the Metabolome of Tomato Plants Infected by Citrus Exocortis Viroid

Benzothiadiazole (BTH) is a functional analogue of the phytohormone salycilic acid (SA) involved in the plant immune response. NahG tomato plants are unable to accumulate SA, which makes them hypersusceptible to several pathogens. Treatments with BTH increase the resistance to bacterial, fungal, viroid, or viral infections. In this study, metabolic alterations in BTH-treated Money Maker and NahG tomato plants infected by citrus exocortis viroid (CEVd) were investigated by nuclear magnetic resonance spectroscopy. Using multivariate data analysis, we have identified defence metabolites induced after viroid infection and BTH-treatment. Glycosylated phenolic compounds include gentisic and ferulic acid accumulated in CEVd-infected tomato plants, as well as phenylalanine, tyrosine, aspartate, glutamate, and asparagine. Besides, an increase of γ-aminobutyric acid (GABA), glutamine, adenosine, and trigonelline, contributed to a clear discrimination between the metabolome of BTH-treated tomato leaves and their corresponding controls. Among them, GABA was the only metabolite significantly accumulated in both genotypes after the chemical treatment. In view of these results, the addition of GABA was performed on tomato plants infected by CEVd, and a reversion of the NahG hypersusceptibility to CEVd was observed, indicating that GABA could regulate the resistance to CEVd induced by BTH.

A practicable strategy for enrichment and separation of four minor flavonoids including two isomers from barley seedlings by macroporous resin column chromatography, medium-pressure LC, and high-speed countercurrent chromatography

Separation of minor compounds especially with similar polarities and structures from complex samples is a challenging work. In the present study, an efficient method was successfully established by macroporous resin column chromatography, medium-pressure liquid chromatography, and high-speed countercurrent chromatography for separation of four minor flavonoids from barley seedlings. Macroporous resin column chromatography and medium-pressure liquid chromatography were used for enrichment of these four flavonoids. High-pressure liquid chromatography analysis showed the total content of these four flavonoids increased from 2.2% in the crude extract to 95.3% in the medium-pressure liquid chromatography fraction. It was indicated that the combination of macroporous resin column chromatography and medium-pressure liquid chromatography could be a practicable strategy for enrichment of minor compounds from complex sample. Then, high-speed countercurrent chromatography was employed for separation of these four flavonoids using ethyl acetate/n-butanol/water (0.1% glacial acetic acid) (4:1:5, v/v/v) as solvent system. As a result, four flavonoids including two isomers with purities higher than 98% were obtained. Interestingly, two flavonoids existing in one high-pressure liquid chromatography peak were also successfully separated. All these indicated high-speed countercurrent chromatography had great potential for separation of compounds with similar structures and polarities. This study provides a reference for efficient enrichment and separation of minor compounds from complex sample.