Influence of exogenous application of glycinebetaine on antioxidative system and growth of salt-stressed soybean seedlings (Glycine max L.)

Transcriptome and Metabolome Analyses Reveal the Molecular Mechanisms of Albizia odoratissima's Response to Drought Stress

Albizia odoratissima is a deciduous tree species belonging to the family Leguminosae. It is widely distributed in the southern subtropical and tropical areas of China and has important ecological and economic value. The growth and metabolic processes of A. odoratissima are affected by drought stress, but the molecular mechanisms remain unknown. Therefore, this study investigated the physicochemical properties, gene expression, and metabolites of A. odoratissima seedlings under drought stress. The results show that, in leaves of A. odoratissima seedlings, drought stress reduced the moisture content, chlorophyll content, photosynthetic efficiency, superoxide dismutase (SOD) activity, and gibberellin (GA) and indoleacetic acid (IAA) contents while increasing the catalase (CAT) and peroxidase (POD) activities and malondialdehyde (MDA), proline, soluble sugar, and soluble protein contents. Within the CK5 (Day 5 of control group) vs. T5 (Day 5 of drought treatment), CK10 vs. T10, CK15 vs. T15, and CK20 vs. T20 groups (CK: control group; T: drought treatment), a total of 676 differentially expressed genes (DEGs) were upregulated and 518 DEGs were downregulated, and a total of 228 and 143 differential accumulation metabolites (DAMs) were identified in the CK10 vs. T10 and CK20 vs. T20 groups. These were mainly involved in the amino acid and alkaloid metabolism pathways in the leaves of the A. odoratissima seedlings. In the amino acid and alkaloid biosynthesis pathways, the relative expression levels of the AoproA (Aod04G002740, ORTHODONTIC APPLIANCE), AoOAT (Aod07G015970, ORNITHINE-OXO-ACID TRANSAMINASE), and AoAOC3 (Aod12G005010/08G003360/05G023920/08G003000/08G003010, AMINE OXIDASE COPPER CONTAINING 3) genes increased, which concurrently promoted the accumulation of arginine, proline, piperine, cadaverine, and lysine. Furthermore, some key transcription factors in the response to drought were identified in the leaves using the weighted gene co-expression network analyses (WGCNA) method. These findings reveal that A. odoratissima seedlings respond to drought stress by improving the capacities of the antioxidant system and secondary metabolism.

The elicitation effects of diode and He-Ne laser irradiations on the alleviation of nutrient-deficiency induced damage in anthocyanin-producing red-fleshed apple cell suspension

PURPOSE

We explored the elicitation role of the laser irradiations on the alleviation of nutrient-deficiency induced damage in anthocyanin-producing red-fleshed apple cell suspension in continuous production of anthocyanin.

METHODS

Anthocyanin-producing red-fleshed apple cells were irradiated by 4 intensity levels of red He-Ne (RHNL) and blue diode (BDL) lasers for 20 min.

RESULTS

Nutrient deficiency indicated negative effect on total soluble proteins (TSP), superoxidase dismutase (SOD) activity, and total phenolics content (TPC) while it displayed a positive effect on malondialdehyde (MDA), total flavonoids content (TFC), O2-, H2O2-, and lipoxygenase (LOX) and polyphenol oxidase (PPO) activities in light controls, illustrating oxidative stress. The laser irradiations on suspension cells indicated variable effects on measured parameters and were time of growth-, levels of intensity-, and laser type-dependent. Likewise, the elicitation effects of lasers relied on a critical threshold among ROS generation and antioxidative system which determines the fate of cells against oxidative stress. The same trend was displayed by RHNL at 6.46 mWcm-2 intensity and BDL at 13.73 mWcm-2. These intensities resulted in a significant increase in SOD, APX, POD, and CAT activities and TSP, TPC, TFC, proline, and glycine betaine accumulation, while induced decrease in LOX, and PPO activities and MDA, and ROS generation, alleviating cellular injury from prolonged nutrient deficiency by diminishing lipid peroxidation and oxidative damages of cell membrane.

CONCLUSION

Results suggested that lasers application on mitigating nutrient deficiency stress relied on establishing a suitable balance between ROS generation and antioxidative system, which enables the nutrient-starved anthocyanin-producing cells to continuously produce anthocyanin.

Specific physiological responses to alkaline carbonate stress in rice (Oryza sativa) seedlings: organic acid metabolism and hormone signalling

In recent years, alkaline soda soil has stimulated numerous biological research on plants under carbonate stress. Here, we explored the difference in physiological regulation of rice seedlings between saline (NaCl) and alkaline carbonate (NaHCO3 and Na2 CO3 ) stress. The rice seedlings were treated with 40mM NaCl, 40mM NaHCO3 and 20mM Na2 CO3 for 2h, 12h, 24h and 36h, their physiological characteristics were determined, and organic acid biosynthesis and metabolism and hormone signalling were identified by transcriptome analysis. The results showed that alkaline stress caused greater damage to their photosynthetic and antioxidant systems and led to greater accumulation of organic acid, membrane damage, proline and soluble sugar but a decreased jasmonic acid content compared with NaCl stress. Jasmonate ZIM-Domain (JAZ), the probable indole-3-acetic acid-amido synthetase GH3s, and the protein phosphatase type 2Cs that related to the hormone signalling pathway especially changed under Na2 CO3 stress. Further, the organic acid biosynthesis and metabolism process in rice seedlings were modified by both Na2 CO3 and NaHCO3 stresses through the glycolate/glyoxylate and pyruvate metabolism pathways. Collectively, this study provides valuable evidence on carbonate-responsive genes and insights into the different molecular mechanisms of saline and alkaline stresses.

Surface modified ZnO NPs by betaine and proline build up tomato plants against drought stress and increase fruit nutritional quality

Drought stress is a serious challenge for global food production. Nanofertilizers and nanocomposites cope with such environmental stresses and also increase nutritional contents of fruits. An in vitro experiment was designed to use Zinc Oxide Nanoparticles (ZnO NPs) primed with Proline and Betaine (ZnOP and ZnOBt NPs) at 50 and 100 mg/kg soil against drought stress in Tomato (Solanum lycopersicum) plants. Plant morphological, biochemical, and fruit nutritional quality were accessed. Maximum plant height was observed under the treatment of ZnOP50 (1.09 m) and ZnO 100 (1.06 m). ZnOP and ZnOBt also improved the chlorophyll content up to 86% and 87.16%, respectively. Application of ZnOP NPs also demonstrated maximum tomato yield (204 g tomato/plant) followed by ZnO NPs and ZnOBt NPs. Nanocomposites decreased phenolics and flavonoids contents in drought stressed plants demonstrating the mitigation of oxidative stress. Nanofertilizer also increased the concentration of phenolics and flavonoids in fruits that increased the nutritional contents. Furthermore a significant accumulation of betaine, proline, and lycopene in fruits on nanocomposite treatment made it nutritional and healthy. Lycopene content increased up to 2.01% and 1.23% in presence of ZnOP50 and ZnOP100, respectively. These outcomes validate that drought stress in plant can be reduced by accumulation of different phytochemicals and quenching oxidative stress. The study deems that nano zinc carrying osmoregulators can greatly reduce the negative effects of drought stress and increase nutritional quality of tomato fruits.

Phytochemical Profiling and Bioactive Potential of Grape Seed Extract in Enhancing Salinity Tolerance of Vicia faba

Salinity stress poses a significant threat to crop productivity worldwide, necessitating effective mitigation strategies. This study investigated the phytochemical composition and potential of grape seed extract (GSE) to mitigate salinity stress effects on faba bean plants. GC-MS analysis revealed several bioactive components in GSE, predominantly fatty acids. GSE was rich in essential nutrients and possessed a high antioxidant capacity. After 14 days of germination, GSE was applied as a foliar spray at different concentrations (0, 2, 4, 6, and 8 g/L) to mitigate the negative effects of salt stress (150 mM NaCl) on faba bean plants. Foliar application of 2-8 g/L GSE significantly enhanced growth parameters such as shoot length, root length, fresh weight, and dry weight of salt-stressed bean plants compared to the control. The Fv/Fm ratio, indicating photosynthetic activity, also improved with GSE treatment under salinity stress compared to the control. GSE effectively alleviated the oxidative stress induced by salinity, reducing malondialdehyde, hydrogen peroxide, praline, and glycine betaine levels. Total soluble proteins, amino acids, and sugars were enhanced in GSE-treated, salt-stressed plants. GSE treatment under salinity stress modulated the total antioxidant capacity, antioxidant responses, and enzyme activities such as peroxidase, ascorbate peroxidase, and polyphenol oxidase compared to salt-stressed plants. Gene expression analysis revealed GSE (6 g/L) upregulated photosynthesis (chlorophyll a/b-binding protein of LHCII type 1-like (Lhcb1) and ribulose bisphosphate carboxylase large chain-like (RbcL)) and carbohydrate metabolism (cell wall invertase I (CWINV1) genes) while downregulating stress response genes (ornithine aminotransferase (OAT) and ethylene-responsive transcription factor 1 (ERF1)) in salt-stressed bean plants. The study demonstrates GSE's usefulness in mitigating salinity stress effects on bean plants by modulating growth, physiology, and gene expression patterns, highlighting its potential as a natural approach to enhance salt tolerance.

Disclosing the effect of exogenous betaine on growth of Suaeda salsa (L.) Pall in the Liaohe coastal wetland, North China

Liaohe coastal wetland has experienced severe degradation of Suaeda salsa (L.) Pall (S. salsa) in recent years. However, the impact of exogenous betaine (GB) on S. salsa growth remains unclear. Therefore, we conducted a natural simulated cultivation in soils of coastal wetland to investigate the effects of GB on S. salsa growth. The results showed that GB increased the height and weight of S. salsa, and meanwhile stimulated the synthesis of endogenous betaine and amino acids, increased soluble sugars and elevated the activity of Na+, K+-ATPase (enhancing osmotic stability). In addition, the activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) increased, and malondialdehyde (MDA) and H2O2 decreased correspondingly, thereby improving the antioxidant capacity. Overall, GB application significantly alleviated salt stress and effectively promoted S. salsa growth. This study first indicated the important role of GB in influencing S. salsa growth, offering potential strategies for remediation in coastal wetlands.

γ-Aminobutyric acid treatment induced chilling tolerance in postharvest peach fruit by upregulating ascorbic acid and glutathione contents at the molecular level

Peach fruit was treated with 5 mM γ-aminobutyric acid (GABA) to further investigate the mechanism by which GABA induced chilling tolerance. Here, we found that GABA not only inhibited the occurrence of chilling injury in peach fruit during cold storage but also maintained fruit quality. Most of the ascorbic acid (AsA) and glutathione (GSH) biosynthetic genes were up-regulated by GABA treatment, and their levels were increased accordingly, thus reducing chilling damage in treated peaches. Meanwhile, the increased transcript of genes in the AsA-GSH cycle by GABA treatment was also related to the induced tolerance against chilling. GABA treatment also increased the expression levels of several candidate ERF transcription factors involved in AsA and GSH biosynthesis. In conclusion, our study found that GABA reduced chilling injury in peach fruit during cold storage due to the higher AsA and GSH contents by positively regulating their modifying genes and candidate transcription factors.

Using Exogenous Melatonin, Glutathione, Proline, and Glycine Betaine Treatments to Combat Abiotic Stresses in Crops

Abiotic stresses, such as drought, salinity, heat, cold, and heavy metals, are associated with global climate change and hamper plant growth and development, affecting crop yields and quality. However, the negative effects of abiotic stresses can be mitigated through exogenous treatments using small biomolecules. For example, the foliar application of melatonin provides the following: it protects the photosynthetic apparatus; it increases the antioxidant defenses, osmoprotectant, and soluble sugar levels; it prevents tissue damage and reduces electrolyte leakage; it improves reactive oxygen species (ROS) scavenging; and it increases biomass, maintains the redox and ion homeostasis, and improves gaseous exchange. Glutathione spray upregulates the glyoxalase system, reduces methylglyoxal (MG) toxicity and oxidative stress, decreases hydrogen peroxide and malondialdehyde accumulation, improves the defense mechanisms, tissue repairs, and nitrogen fixation, and upregulates the phytochelatins. The exogenous application of proline enhances growth and other physiological characteristics, upregulates osmoprotection, protects the integrity of the plasma lemma, reduces lipid peroxidation, increases photosynthetic pigments, phenolic acids, flavonoids, and amino acids, and enhances stress tolerance, carbon fixation, and leaf nitrogen content. The foliar application of glycine betaine improves growth, upregulates osmoprotection and osmoregulation, increases relative water content, net photosynthetic rate, and catalase activity, decreases photorespiration, ion leakage, and lipid peroxidation, protects the oxygen-evolving complex, and prevents chlorosis. Chemical priming has various important advantages over transgenic technology as it is typically more affordable for farmers and safe for plants, people, and animals, while being considered environmentally acceptable. Chemical priming helps to improve the quality and quantity of the yield. This review summarizes and discusses how exogenous melatonin, glutathione, proline, and glycine betaine can help crops combat abiotic stresses.

Hydrogen peroxide priming alleviates salinity induced toxic effect in maize by improving antioxidant defense system, ionic homeostasis, photosynthetic efficiency and hormonal crosstalk

BACKGROUND

Salinity stress (SS) is a serious detrimental factor for crop growth and productivity and its intensity it is continuously increasing which is posing serious threat to global food security. Hydrogen peroxide (H₂O₂) priming has emerged as an excellent strategy to mitigate the adverse impacts of SS. However, the role of H₂O₂ priming in mitigating the salinity induced toxicity is not fully explored.

METHODS AND RESULTS

Therefore, in this context the present study was conducted in complete randomized design (CRD) in factorial combination to determine the impact of H₂O₂ priming on germination, growth, physiological and biochemical traits, osmo-regulating compounds, hormonal balance and ionic homeostasis. The experiment was based on different levels of SS; control, 6 and 12 dS m^-1 SS and priming treatments, control and H₂O₂ priming (2%). Salinity stress significantly reduced the growth, leaf water status (- 15.55%), calcium (Ca²⁺), potassium (K⁺) and magnesium (Mg²⁺) accumulation and increased malondialdehyde (MDA: + 29.95%), H₂O₂ (+ 21.48%) contents, osmo-regulating compounds (proline, soluble sugars), indole acetic acid (IAA), anti-oxidant activities (ascorbate peroxidase: APX, catalase: CAT, peroxidase: POD and ascorbic acid: AsA) and accumulation of sodium (Na⁺) and chloride (Cl^-.). H₂O₂ priming effectively reduced the effects of SS on germination and growth and strengthen the anti-oxidant activities through reduced MDA (- 12.36%) and H₂O₂ (- 21.13%) and increasing leaf water status (16.90%), soluble protein (+ 71.32%), free amino acids (+ 26.41%), proline (+ 49.18%), soluble sugars (+ 71.02%), IAA (+ 57.59%) and gibberlic acid (GA) (+ 21.11%). Above all, H₂O₂ priming reduced the massive entry of noxious ions (Na⁺ and Cl^-) while increased the entry of Ca²⁺, K⁺ and Mg²⁺ thus improved the plant performance under SS.

CONCLUSION

In conclusion H₂O₂ priming was proved beneficial for improving maize growth under SS thorough enhanced anti-oxidant activities, photosynthetic pigments, leaf water status, accumulation of osmo-regulating compounds, hormonal balance and ionic homeostasis.

Exogenous Glycine Betaine Application Improves Freezing Tolerance of Cabbage (Brassica oleracea L.) Leaves

Exogenous glycine betaine (GB) application has been reported to improve plant tolerance to various abiotic stresses, but its effect on freezing tolerance has not been well studied. We investigated the effect of exogenous GB on freezing tolerance of cabbage (Brassica oleracea L.) leaves. Seedlings fed with 30 mM GB via sub-irrigation showed effectively assimilated GB as evident by higher GB concentration. Exogenous GB did not retard leaf-growth (fresh weight, dry weight, and leaf area) rather slightly promoted it. Temperature controlled freeze-thaw tests proved GB-fed plants were more freeze-tolerant as indicated by lower electrolyte leakage (i.e., indication of less membrane damage) and alleviating oxidative stress (less accumulation of O₂^•- and H₂O₂, as well as of malondialdehyde (MDA)) following a relatively moderate or severe freeze-thaw stress, i.e., -2.5 and -3.5 °C. Improved freezing tolerance induced by exogenous GB application may be associated with accumulation of compatible solute (proline) and antioxidant (glutathione). GB-fed leaves also had higher activity of antioxidant enzymes, catalase (CAT), ascorbate peroxidase (APX), and superoxide dismutase (SOD). These changes, together, may improve freezing tolerance through membrane protection from freeze-desiccation and alleviation of freeze-induced oxidative stress.

Niche differentiation of belowground microorganisms and their functional signatures in Assam type tea (Camellia sinensis var. assamica)

We employed an Illumina-based high-throughput metagenomics sequencing approach to unveil the rhizosphere and root endosphere microbial community associated with an organically grown Camellia population located at the Experimental Garden for Plantation Crops, Assam (India). The de novo assembled tea root endosphere metagenome contained 24,231 contigs (total 7,771,089 base pairs with an average length of 321 bps), while tea rhizosphere soil metagenome contained 261,965 sequences (total 230,537,174 base pairs, average length 846). The most prominent rhizobacteria belonged to the genera, viz., Bacillus (10.35%), Candidatus Solibacter (6.36%), Burkholderia (5.19%), Pseudomonas (3.9%), Streptomyces (3.52%), and Bradyrhizobium (2.77%), while the root endosphere was dominated by bacterial genera, viz., Serratia (46.64%), Methylobacterium (8.02%), Yersinia (5.97%), Burkholderia (2.05%), etc. The presence of few agronomically important bacterial genera, Bradyrhizobium, Rhizobium (each 0.93%), Sinorhizobium (0.34%), Azorhizobium, and Flavobacterium (0.17% each), was also detected in the root endosphere. KEGG pathway mapping indicated the presence of microbial metabolic pathway genes related to tyrosine metabolism, tryptophan metabolism, glyoxylate, and dicarboxylate metabolism which play important roles in endosphere activities, including survival, growth promotion, and host adaptation. The root endosphere microbiome also contained few important plant growth promoting traits related to phytohormone production, abiotic stress alleviation, mineral solubilization, and plant disease suppression.

Control of Elevated Ion Accumulation, Oxidative Stress, and Lipid Peroxidation with Salicylic Acid-Induced Accumulation of Glycine Betaine in Salinity-Exposed Vigna radiata L

The identification of the sustainable approaches is required for the minimization of adverse impact of worldwide increasing soil salinity on plant growth, development, and productivity. This study investigated the protective role and major mechanism underlying salicylic acid (SA; 0.1, 0.5, or 1.0 mM)-induced glycine betaine (GB)-mediated tolerance to salinity (50 mM NaCl) in mungbean (Vigna radiata L. cultivar Punt Mung). The supply of 0.5 mM SA maximally increased the accumulation of GB (>40%) with respect to the control. This was further corroborated with the increase in water potential, antioxidant system (reduced glutathione (GSH), GSH/GSSG redox state, and glutathione reductase (GR) activity) and decreased Na+ and Cl- accumulation, Na+/K+ ratio, oxidative stress, and lipid peroxidation. This was also associated with the increased photosynthesis (14-18%) and growth (7-12%) parameters. Overall, SA-induced accumulation of GB protected photosynthesis and growth against 50 mM NaCl-accrued impacts in V. radiata through minimizing the accumulation of Na+ and Cl- ions, oxidative stress, and maintaining high GSH level that led to reduced cellular redox environment.

Understanding the roles of osmolytes for acclimatizing plants to changing environment: a review of potential mechanism

Abiotic stresses are significant environmental issues that restrict plant growth, productivity, and survival while also posing a threat to global food production and security. Plants produce compatible solutes known as osmolytes to adapt themselves in such changing environment. Osmolytes contribute to homeostasis maintenance, provide the driving gradient for water uptake, maintain cell turgor by osmotic adjustment, and redox metabolism to remove excess level of reactive oxygen species (ROS) and reestablish the cellular redox balance as well as protect cellular machinery from osmotic stress and oxidative damage. Perceiving the mechanisms how plants interpret environmental signals and transmit them to cellular machinery to activate adaptive responses is important for crop improvement programs to get stress-tolerant varieties. A large number of studies conducted in the last few decades have shown that osmolytes accumulate in plants and have strong associations with abiotic stress tolerance. Production of abundant osmolytes is needed for tolerance in many plant species. In addition, transgenic plants overexpressing genes for different osmolytes showed enhanced tolerance to various abiotic stresses. Many important aspects of their mechanisms of action are yet to be largely identified, especially regarding the relevance and relative contribution of specific osmolytes to the stress tolerance of a given species. Therefore, more efforts and resources should be invested in the study of the abiotic stress responses of plants in their natural habitats. The present review focuses on the possible roles and mechanisms of osmolytes and their association toward abiotic stress tolerance in plants. This review would help the readers in learning more about osmolytes and how they behave in changing environments as well as getting an idea of how this knowledge could be applied to develop stress tolerance in plants.

Glycine betaine functionalized graphene oxide as a new engineering nanoparticle lessens salt stress impacts in sweet basil (Ocimum basilicum L.)

Regarding destructive impacts of salinity on different vital processes of plants, many strategies have been developed to alleviate salinity effects. Amongst, nanoparticles (NPs) application has been achieved great attention. For that point, considering positive effects of graphene oxide NPs (GO) and glycine betaine (GB) on different plant processes, GO-GB NPs were primarily synthesized to use GO as a carrier for GB. Then, GO, GB and GO-GB (each in three concentrations; 0, 50 and 100 mg L^-1) were applied on sweet basil (Ocimum basilicum L.) plants under 0, 50 and 100 mM salinity stress conditions. The results demonstrated that GO-GB NPs could lessen negative effects of salinity by enhancing agronomic traits, photosynthetic pigments, chlorophyll fluorescence parameters, membrane stability index (MSI), proline, phenols, antioxidant enzymes activities and dominant constituents of essential oils and decreasing MDA and H₂O₂. These positive effects were more considerable at its lower dose (50 mg L^-1) introducing it as the best treatment to ameliorate sweet basil performance especially essential oil compounds under salt stress. GO application at its higher dose (100 mg L^-1) demonstrated toxicity by negative impacts on the measured parameters. In conclusion, the positive response of sweet basil to GO-GB NPs under non-stress and salt stress conditions cause to consider the NPs as potential novel plant growth promoting and stress protecting agent with innovative outlooks for its use in agriculture.

Bioregulators: unlocking their potential role in regulation of the plant oxidative defense system

Plant bioregulators play an important role in managing oxidative stress tolerance in plants. Utilizing their ability in stress sensitive crops through genetic engineering will be a meaningful approach to manage food production under the threat of climate change. Exploitation of the plant defense system against oxidative stress to engineer tolerant plants in the climate change scenario is a sustainable and meaningful strategy. Plant bioregulators (PBRs), which are important biotic factors, are known to play a vital role not only in the development of plants, but also in inducing tolerance in plants against various environmental extremes. These bioregulators include auxins, gibberellins, cytokinins, abscisic acid, brassinosteroids, polyamines, strigolactones, and ascorbic acid and provide protection against the oxidative stress-associated reactive oxygen species through modulation or activation of a plant's antioxidant system. Therefore, exploitation of their functioning and accumulation is of considerable significance for the development of plants more tolerant of harsh environmental conditions in order to tackle the issue of food security under the threat of climate change. Therefore, this review summarizes a new line of evidence that how PBRs act as inducers of oxidative stress resistance in plants and how they could be modulated in transgenic crops via introgression of genes. Reactive oxygen species production during oxidative stress events and their neutralization through an efficient antioxidants system is comprehensively detailed. Further, the use of exogenously applied PBRs in the induction of oxidative stress resistance is discussed. Recent advances in engineering transgenic plants with modified PBR gene expression to exploit the plant defense system against oxidative stress are discussed from an agricultural perspective.

Gly Betaine Surpasses Melatonin to Improve Salt Tolerance in Dalbergia odorifera

Salinity is one of the most serious factors limiting plant growth which can provoke significant losses in agricultural crop production, particularly in arid and semi-arid areas. This study aimed to investigate whether melatonin (MT; 0.05 and 0.1 mM), which has pleiotropic roles, has a better effect than glycine betaine (GB; 10 and 50 mM) on providing salt tolerance in a woody plant Dalbergia odorifera T. Chen. Also, the alternative oxidase activity (AOX) in plant subjected to MT or GB under salinity (150 and 250 mM) was evaluated given that the effect of exogenous MT or GB on AOX has not been reported yet. The results showed that the exogenous application of GB on the seedlings of D. odorifera increased the plant growth parameters, relative water content, total of chlorophyll content, and carotenoid content compared with well-watered and MT treatments. Under severe salinity, the seedlings subjected to GB showed, a significant enhancement in water use efficiency, transpiration, and net photosynthetic rate regardless to MT-treated seedlings. The levels of proline and soluble sugar in the seedlings treated with MT or GB decreased significantly under mild and severe salinity correlated with those in salt-stressed seedlings. Furthermore, GB-treated plants exhibited a significant inhibition of malondialdehyde content compared with MT-treated plants. The concentration of thiols and phenolic compounds were significantly enhanced in the leaves of seedlings treated with MT compared with those treated with GB. Under salt stress condition, GB scavenged significantly higher levels of hydrogen peroxide than MT; while under severe salinity, plants subjected to MT showed better scavenging ability for hydroxyl radicals compared with GB-treated seedlings. The results demonstrated also an enhancement of the levels of superoxide dismutase (SOD), guaiacol peroxidase, and AOX activities in seedlings treated with GB or MT compared with salt-stressed plants. The catalase activity (CAT) was increased by 0.05 mM MT and 0.1 mM GB under mild salinity. Meanwhile, the AOX activity under severe salinity was enhanced only by GB 50 mM. The findings of this study suggested that GB-treated seedlings possessed a better salt tolerance in comparison with MT-treated seedlings.

Comparative analysis of two phytochrome mutants of tomato (Micro-Tom cv.) reveals specific physiological, biochemical, and molecular responses under chilling stress

Background

Phytochromes are plant photoreceptors that have long been associated with photomorphogenesis in plants; however, more recently, their crucial role in the regulation of variety of abiotic stresses has been explored. Chilling stress is one of the abiotic factors that severely affect growth, development, and productivity of crops. In the present work, we have analyzed and compared physiological, biochemical, and molecular responses in two contrasting phytochrome mutants of tomato, namely aurea (aur) and high pigment1 (hp1), along with wild-type cultivar Micro-Tom (MT) under chilling stress. In tomato, aur is phytochrome-deficient mutant while hp1 is a phytochrome-sensitive mutant. The genotype-specific physiological, biochemical, and molecular responses under chilling stress in tomato mutants strongly validated phytochrome-mediated regulation of abiotic stress.

Results

Here, we demonstrate that phytochrome-sensitive mutant hp1 show improved performance compared to phytochrome-deficient mutant aur and wild-type MT plants under chilling stress. Interestingly, we noticed significant increase in several photosynthetic-related parameters in hp1 under chilling stress that include photosynthetic rate, stomatal conductance, stomatal aperture, transpiration rate, chlorophyll a and carotenoids. Whereas most parameters were negatively affected in aur and MT except a slight increase in carotenoids in MT plants under chilling stress. Further, we found that PSII quantum efficiency (Fv/Fm), PSII operating efficiency (Fq′/Fm′), and non-photochemical quenching (NPQ) were all positively regulated in hp1, which demonstrate enhanced photosynthetic performance of hp1 under stress. On the other hand, Fv/Fm and Fq′/Fm′ were decreased significantly in aur and wild-type plants. In addition, NPQ was not affected in MT but declined in aur mutant after chilling stress. Noticeably, the transcript analysis show that PHY genes which were previously reported to act as molecular switches in response to several abiotic stresses were mainly induced in hp1 and repressed in aur and MT in response to stress. As expected, we also found reduced levels of malondialdehyde (MDA), enhanced activities of antioxidant enzymes, and higher accumulation of protecting osmolytes (soluble sugars, proline, glycine betaine) which further elaborate the underlying tolerance mechanism of hp1 genotype under chilling stress.

Conclusion

Our findings clearly demonstrate that phytochrome-sensitive and phytochrome-deficient tomato mutants respond differently under chilling stress thereby regulating physiological, biochemical, and molecular responses and thus establish a strong link between phytochromes and their role in stress tolerance.

Supplementary Information

The online version contains supplementary material available at 10.1186/s43141-020-00091-1.

Secondary Metabolites From Halotolerant Plant Growth Promoting Rhizobacteria for Ameliorating Salinity Stress in Plants

Soil salinization has emerged as one of the prime environmental constraints endangering soil quality and agricultural productivity. Anthropogenic activities coupled with rapid pace of climate change are the key drivers of soil salinity resulting in degradation of agricultural lands. Increasing levels of salt not only impair structure of soil and its microbial activity but also restrict plant growth by causing harmful imbalance and metabolic disorders. Potential of secondary metabolites synthesized by halotolerant plant growth promoting rhizobacteria (HT-PGPR) in the management of salinity stress in crops is gaining importance. A wide array of secondary metabolites such as osmoprotectants/compatible solutes, exopolysaccharides (EPS) and volatile organic compounds (VOCs) from HT-PGPR have been reported to play crucial roles in ameliorating salinity stress in plants and their symbiotic partners. In addition, HT-PGPR and their metabolites also help in prompt buffering of the salt stress and act as biological engineers enhancing the quality and productivity of saline soils. The review documents prominent secondary metabolites from HT-PGPR and their role in modulating responses of plants to salinity stress. The review also highlights the mechanisms involved in the production of secondary metabolites by HT-PGPR in saline conditions. Utilizing the HT-PGPR and their secondary metabolites for the development of novel bioinoculants for the management of saline agro-ecosystems can be an important strategy in the future.

Glycine betaine counters salinity stress by maintaining high K+/Na+ ratio and antioxidant defense via limiting Na+ uptake in common bean (Phaseolus vulgaris L.)

This paper reports the role of exogenous glycine betaine (25 and 50 mM GB at a rate of 50 mL per plant) in enhancing NaCl-stress tolerance in common bean (Phaseolus vulgaris L.). Irrigating plants by simulated saline water, containing 0, 50 and 100 mM sodium chloride (NaCl), significantly reduced the growth dynamics, photosynthetic pigments (i.e., Chl a, Chl b, and carotenoids), membrane stability index (MSI), relative water content (RWC), and pod yield. While, malondialdehyde (MDA), endogenous proline, and glutathione contents, electrolyte leakage (EL), antioxidant defense system, and Na⁺ accumulation markedly increased upon exposure to NaCl-stress. However, the application of exogenous GB significantly improved salt tolerance of common bean as it increased the antioxidant defense including both enzymatic (i.e., peroxidase, superoxide dismutase, and catalase) and nonenzymatic (i.e., proline and glutathione) agents. Consequently, MSI, RWC, EL, and photosynthetic pigments have been improved recording significantly higher values than the control. Moreover, the pod yield increased by 29.8 and 59.4% when plants grown under 50 and 100 mM NaCl, respectively, were sprayed with 25 mM GB. Our results show that GB-induced slat tolerance in common bean plants mainly depends on the osmoregulation effect of GB and to a lesser extent on its antioxidant capacity. Foliar application of GB significantly reduced the accumulation of Na⁺ and at the same time induced K⁺ uptake maintaining a higher K⁺/Na⁺ ratio. Despite some changes in the activities of antioxidant enzymes induced by the application of GB, no consistent contribution in the salt tolerance could be cited in this study. Therefore, we suggest that salt tolerance is largely unrelated to the antioxidant defense ability of GB in common bean. While the potential role of GB in ameliorating salt tolerance is mainly due to the adjustment of ions uptake through limiting Na⁺ uptake and alternatively increasing K⁺ accumulation in plant tissues.

Glycine Betaine Accumulation, Significance and Interests for Heavy Metal Tolerance in Plants

Unexpected biomagnifications and bioaccumulation of heavy metals (HMs) in the surrounding environment has become a predicament for all living organisms together with plants. Excessive release of HMs from industrial discharge and other anthropogenic activities has threatened sustainable agricultural practices and limited the overall profitable yield of different plants species. Heavy metals at toxic levels interact with cellular molecules, leading towards the unnecessary generation of reactive oxygen species (ROS), restricting productivity and growth of the plants. The application of various osmoprotectants is a renowned approach to mitigate the harmful effects of HMs on plants. In this review, the effective role of glycine betaine (GB) in alleviation of HM stress is summarized. Glycine betaine is very important osmoregulator, and its level varies considerably among different plants. Application of GB on plants under HMs stress successfully improves growth, photosynthesis, antioxidant enzymes activities, nutrients uptake, and minimizes excessive heavy metal uptake and oxidative stress. Moreover, GB activates the adjustment of glutathione reductase (GR), ascorbic acid (AsA) and glutathione (GSH) contents in plants under HM stress. Excessive accumulation of GB through the utilization of a genetic engineering approach can successfully enhance tolerance against stress, which is considered an important feature that needs to be investigated in depth.

Revealing Further Insights on Chilling Injury of Postharvest Bananas by Untargeted Lipidomics

Chilling injury is especially prominent in postharvest bananas stored at low temperature below 13 °C. To elucidate better the relationship between cell membrane lipids and chilling injury, an untargeted lipidomics approach using ultra-performance liquid chromatography-mass spectrometry was conducted. Banana fruit were stored at 6 °C for 0 (control) and 4 days and then sampled for lipid analysis. After 4 days of storage, banana peel exhibited a marked chilling injury symptom. Furthermore, 45 lipid compounds, including glycerophospholipids, saccharolipids, and glycerolipids, were identified with significant changes in peel tissues of bananas stored for 4 days compared with the control fruit. In addition, higher ratio of digalactosyldiacylglycerol (DGDG) to monogalactosyldiacylglycerol (MGDG) and higher levels of phosphatidic acid (PA) and saturated fatty acids but lower levels of phosphatidylcholine (PC), phosphatidylethanolamine (PE), and unsaturated fatty acids were observed in banana fruit with chilling injury in contrast to the control fruit. Meanwhile, higher activities of phospholipase D (PLD) and lipoxygenase (LOX) were associated with significantly upregulated gene expressions of MaPLD1 and MaLOX2 and higher malondialdehyde (MDA) content in chilling injury-related bananas. In conclusion, our study indicated that membrane lipid degradation resulted from reduced PC and PE, but accumulated PA, while membrane lipid peroxidation resulted from the elevated saturation of fatty acids, resulting in membrane damage which subsequently accelerated the chilling injury occurrence of banana fruit during storage at low temperature.

Improving Regulation of Enzymatic and Non-Enzymatic Antioxidants and Stress-Related Gene Stimulation in Cucumber mosaic cucumovirus-Infected Cucumber Plants Treated with Glycine Betaine, Chitosan and Combination

Cucumber mosaic cucumovirus (CMV) is a deadly plant virus that results in crop-yield losses with serious economic consequences. In recent years, environmentally friendly components have been developed to manage crop diseases as alternatives to chemical pesticides, including the use of natural compounds such as glycine betaine (GB) and chitosan (CHT), either alone or in combination. In the present study, the leaves of the cucumber plants were foliar-sprayed with GB and CHT—either alone or in combination—to evaluate their ability to induce resistance against CMV. The results showed a significant reduction in disease severity and CMV accumulation in plants treated with GB and CHT, either alone or in combination, compared to untreated plants (challenge control). In every treatment, growth indices, leaf chlorophylls content, phytohormones (i.e., indole acetic acid, gibberellic acid, salicylic acid and jasmonic acid), endogenous osmoprotectants (i.e., proline, soluble sugars and glycine betaine), non-enzymatic antioxidants (i.e., ascorbic acid, glutathione and phenols) and enzymatic antioxidants (i.e., superoxide dismutase, peroxidase, polyphenol oxidase, catalase, lipoxygenase, ascorbate peroxidase, glutathione reductase, chitinase and β-1,3 glucanase) of virus-infected plants were significantly increased. On the other hand, malondialdehyde and abscisic acid contents have been significantly reduced. Based on a gene expression study, all treated plants exhibited increased expression levels of some regulatory defense genes such as PR1 and PAL1. In conclusion, the combination of GB and CHT is the most effective treatment in alleviated virus infection. To our knowledge, this is the first report to demonstrate the induction of systemic resistance against CMV by using GB.

Traditional rice landraces in Lei-Qiong area of South China tolerate salt stress with strong antioxidant activity

Salt stress, causing serious loss on crop productions, is one of the most important environmental stresses throughout the world. The aim of this study is to select salt-tolerant traditional rice resources collected from Lei-Qiong area of South China and investigate their physiological performances and biochemical regulations during salt stress response, together with two well-known international varieties, Nona Bokra (salt-tolerant sample) and IR29 (salt-sensitive sample). After comprehensive analyses, we discovered that two Lei-Qiong traditional salt-tolerant rice samples showed less growth inhibition by salt stress during both germination and seedling stage, in comparison with other rice samples. Moreover, there were less chlorosis symptoms in these two kinds of salt tolerant rice under salt stress, corresponding to their better water-holding capacity. We measured malondialdehyde and proline contents, and activities of CAT and POD of seedlings treated with 100 mM NaCl for 5 dand 10 d, respectively. Interestingly, less cellular membrane damage and stronger antioxidant enzyme system were found in the two Lei-Qiong rice samples. Our study suggests that traditional rice landrace growing onshore of Lei-Qiong area in China possesses good salt-tolerant capacity, which could be attributed to their efficient antioxidant enzyme system.

Exogenously Applied Ascorbic Acid-Mediated Changes in Osmoprotection and Oxidative Defense System Enhanced Water Stress Tolerance in Different Cultivars of Safflower (Carthamus tinctorious L.)

The present study was conducted to examine the effect of exogenously applied ascorbic acid (AsA) on osmoprotectants and the oxidative defense system in four cultivars (16171, 16183, 16207 and 16246) of safflower under well-watered and water deficit conditions. Water stress (60% field capacity) significantly decreased the shoot and root fresh and dry weights, shoot and root lengths and chlorophyll contents in all four safflower cultivars, while it increased the leaf free proline, total phenolics, total soluble proteins, hydrogen peroxide content and activities of catalase, superoxide dismutase and peroxidase enzymes. Foliar-applied (100 mg L-1 and 150 mg L-1) ascorbic acid caused a marked improvement in shoot and root fresh and dry weights, plant height, chlorophyll and AsA contents as well as the activity of peroxidase (POD) enzyme particularly under water deficit conditions. It also increased the accumulation of leaf proline, total phenolics, total soluble proteins and glycine betaine (GB) content in all four cultivars. Exogenously applied AsA lowered the contents of MDA and H2O2, and the activities of CAT and SOD enzymes. Overall, exogenously applied AsA had a positive effect on the growth of safflower plants under water deficit conditions which could be related to AsA-induced enhanced osmoprotection and regulation of antioxidant defense system.

Physiological response of Secale cereale L. seedlings under freezing-thawing and alkaline salt stress

Freezing-thawing and saline-alkaline are the major abiotic stress for the pasture in most high-latitude areas, which are serious threats to the yield of pasture. In this study, the osmotic adjustment substances, membrane lipid peroxidation, and antioxidant enzymes activities of rye (Secale cereale L., cv. Dongmu-70) seedlings under different treatments: CK (no treatment), SC (Na₂CO₃ treatment), FT (freezing-thawing treatment), and FT+SC (combined Na₂CO₃ and freezing-thawing treatments), were investigated. At the freezing stage, the content of MDA and proline, the activity of APX, SOD, and POD increased with the decrease of the temperature in the leaves of rye seedlings in FT and FT+SC treatments and reached the maximum value at - 5 °C. In addition, the content of protein and H₂O₂, CAT activity reached the maximum value at 0 °C; the damage is larger under low temperature stress at 0 °C and - 5 °C in rye seedling. At the thawing stage, the content of MDA and H₂O₂ in seedling leaves decreased in FT and FT + SC treatments. These results demonstrated that proline content and antioxidant enzymes activities could play an important role in protecting cytomembrane and scavenging ROS respectively in rye under alkaline salt stress and freezing-thawing stress. The result also indicated rye seedlings were subjected to a freezing-thawing stress which resulted in a reversible (recoverable) injury.

Spatial and Temporal Profile of Glycine Betaine Accumulation in Plants Under Abiotic Stresses

Several halophytes and a few crop plants, including Poaceae, synthesize and accumulate glycine betaine (GB) in response to environmental constraints. GB plays an important role in osmoregulation, in fact, it is one of the main nitrogen-containing compatible osmolytes found in Poaceae. It can interplay with molecules and structures, preserving the activity of macromolecules, maintaining the integrity of membranes against stresses and scavenging ROS. Exogenous GB applications have been proven to induce the expression of genes involved in oxidative stress responses, with a restriction of ROS accumulation and lipid peroxidation in cultured tobacco cells under drought and salinity, and even stabilizing photosynthetic structures under stress. In the plant kingdom, GB is synthesized from choline by a two-step oxidation reaction. The first oxidation is catalyzed by choline monooxygenase (CMO) and the second oxidation is catalyzed by NAD+-dependent betaine aldehyde dehydrogenase. Moreover, in plants, the cytosolic enzyme, named N-methyltransferase, catalyzes the conversion of phosphoethanolamine to phosphocholine. However, changes in CMO expression genes under abiotic stresses have been observed. GB accumulation is ontogenetically controlled since it happens in young tissues during prolonged stress, while its degradation is generally not significant in plants. This ability of plants to accumulate high levels of GB in young tissues under abiotic stress, is independent of nitrogen (N) availability and supports the view that plant N allocation is dictated primarily to supply and protect the growing tissues, even under N limitation. Indeed, the contribution of GB to osmotic adjustment and ionic and oxidative stress defense in young tissues, is much higher than that in older ones. In this review, the biosynthesis and accumulation of GB in plants, under several abiotic stresses, were analyzed focusing on all possible roles this metabolite can play, particularly in young tissues.

Identification of GB1, a gene whose constitutive overexpression increases glycinebetaine content in maize and soybean

Efforts to increase glycinebetaine (GB) levels in plants have been pursued as an approach to improving plant performance under stress conditions. To date, the impact of engineered levels of GB has been limited by metabolic constraints that restrict the achieved increases. We report the identification of a novel gene, GB1, that is differentially expressed in high and low GB accumulating maize genotypes. The predicted GB1 protein shows 60% identity to a putative C-4 sterol methyl oxidase from rice. Overexpression of GB1 in maize and soybean led to dramatically higher leaf GB content in most of the transgenic lines compared to wild-type. These results suggest that the GB1 protein is an important component of the biochemical pathways controlling GB accumulation in plants.

Gene Expression Characteristics and Regulation Mechanisms of Superoxide Dismutase and Its Physiological Roles in Plants under Stress

Superoxide dismutases (SODs) are key enzymes functioning as the first line of antioxidant defense by virtue of the ability to convert highly reactive superoxide radicals to hydrogen peroxide and molecular oxygen. SOD plays a central role in protecting plants against the toxic effects of reactive oxygen species generated during normal cellular metabolic activity or as a result of various environmental stresses. Our review focuses on the characteristics of expression of SOD genes, the mechanisms regulating expression of SOD genes at transcriptional, posttranscriptional, and translation levels, and their functional role(s) during development and in response to biotic or abiotic stresses. We propose two important research directions: studying SOD at the genome-wide or proteome-wide level, and improving plant stress tolerances by selecting varieties using transgenic technology.

Analysis of effects of a new environmental pollutant, bisphenol A, on antioxidant systems in soybean roots at different growth stages

Bisphenol A (BPA) is an important industrial raw material. Because of its widespread use and increasing release into environment, BPA has become a new environmental pollutant. Previous studies about BPA's effects in plants focus on a certain growth stage. However, the plant's response to pollutants varies at different growth stages. Therefore, in this work, BPA's effects in soybean roots at different growth stages were investigated by determining the reactive oxygen species levels, membrane lipid fatty acid composition, membrane lipid peroxidation, and antioxidant systems. The results showed that low-dose BPA exposure slightly caused membrane lipid peroxidation but didn't activate antioxidant systems at the seedling stage, and this exposure did not affect above process at other growth stages; high-dose BPA increased reactive oxygen species levels and then caused membrane lipid peroxidation at all growth stages although it activated antioxidant systems, and these effects were weaker with prolonging the growth stages. The recovery degree after withdrawal of BPA exposure was negatively related to BPA dose, but was positively related to growth stage. Taken together, the effects of BPA on antioxidant systems in soybean roots were associated with BPA exposure dose and soybean growth stage.