Search

The coordination between phytohormones regulation, stomatal behaviour (stomatal index and opening/closing) and gas exchange are potent determinants of plant survival under drought stress. However, we found a knowledge gap in the mechanism regulating the fine-tuning of these features during drought. In order to address this we evaluated gas exchange, stomatal behaviour and endogenous phytohormones content in two cotton varieties (LRA-5166 and NBRI-67) differing in drought sensitivity during water deficit conditions. Variety specific differences were recorded in net photosynthesis rate (A), transpiration rate (E) and stomatal conductance (gs) with significantly less decrease in drought tolerant LRA-5166 than drought sensitive NBRI-67. The abscisic acid (ABA) accumulation was significantly increased in LRA-5166 while reduced in NBRI-67 under water deficit, which was accompanied by relatively less reduced 6-benzylaminopurine (6-BAP) level in LRA-5166 than NBRI-67. Thus, improved ABA/6-BAP ratio was observed in both the varieties of cotton. Critically, LRA-5166 has reduced stomatal index, aperture size and significantly higher A and intrinsic water use efficiency (WUEi), thus higher drought tolerance than NBRI-67. Furthermore, we found that endogenous ABA predominantly maintains the stomatal behaviour and regulates its physiology either by antagonizing 6-BAP or alone to coordinate with water deficit signals. Overall, our findings describe a new insight as to how drought modulates endogenous ABA and 6-BAP homeostasis in cotton leaf and the mechanism of stomatal regulation by ABA and 6-BAP in cotton. [ABSTRACT FROM AUTHOR]

The present study aims to explore the alternative way to improve the quality and productivity of rice grown under CO2 stress through an external supplement of Trichoderma as a biofertilizer (BF). The impact of BF-treated rice under elevated CO2 (eCO2) was examined by different plant growth parameters, physiological observations, scanning electron microscopy, microbial community profiling and expression levels of stress-related genes. The effect of eCO2 on percent change in yielding attributes of rice (Heena and Kiran) was found higher in control, whereas it was reduced in the presence of BF. Photosynthetic rate, stomatal conductance and transpiration rate were higher in BF-treated rice under eCO2 condition. SEM analysis of BF-treated roots exhibits an increase in the number of metaxylem along with its diameter with thicker and rigid sclerenchymatous cells. Expression analysis of stress-related genes showed an increase in their mRNA transcripts under eCO2 condition. A significant change in the microbial community was found in the rhizospheric region of Heena treated with BF under eCO2. The current study demonstrates the potential of BF in ameliorating the stress generated as a result of CO2 enrichment. [ABSTRACT FROM AUTHOR]

Glutaredoxins (Grxs) are small (10–15 kDa) glutathione (GSH) - dependent redox proteins. The role of Grxs are well documented in tolerance to heavy metal stress in prokaryotic and mammalian systems and a few plant genera, but is poorly understood in plants against drought. In the present study, two rice glutaredoxin (Osgrx) genes (LOC_Os02g40500 and LOC_Os01g27140) responsible for tolerance against heavy metal stress have been studied for investigating their role against drought. Each glutaredoxin gene was over-expressed in Arabidopsis thaliana to reveal their role in drought stress. The relative expression of both Osgrx genes was higher in the transgenic lines. Transgenic lines of both Osgrxs showed longer roots, higher seed germination, and survival efficiency during drought stress. The physiological parameters (P N , g s , E , WUE, q P, NPQ and ETR), antioxidant enzymes (GRX, GR, GPX, GST, APX, POD, SOD, CAT, DHAR, and MDHAR), antioxidant molecules (ascorbate and GSH) and stress-responsive amino acids (cysteine and proline) levels were additionally increased in transgenic lines of both Osgrxs to provide drought tolerance. The outcomes from this study strongly determined that each Osgrx gene participated in the moderation of drought and might be utilized in biological engineering strategies to overcome drought conditions in different crops. • LOC_Os02g40500 and LOC_Os01g27140 reduced the ROS generated under drought stress. • Osgrxs enhanced the level of the antioxidant molecules, antioxidant enzymes, and stress responsible amino acids. • Osgrxs enhanced the various physiological parameters against drought stress and protected the plant from damage. • Osgrxs enhanced the RWC and reduced the stress markers. [ABSTRACT FROM AUTHOR]

Glutaredoxins (Grxs) are small multifunctional redox proteins. Grxs have glutathione-dependent oxidoreductase activity in the presence of glutathione reductase and NADPH. The role of Grxs is well studied in heavy metal tolerance in prokaryotic and mammalian systems but not in plant genera. In the present study, a chickpea glutaredoxin (CaGrx) gene (LOC101493651) has been investigated against metal stress based on its primary screening in chickpea which revealed higher up-regulation of CaGrx gene under various heavy metals (AsIII-25 μM, AsV-250 μM, Cr(VI)-300 μM, and Cd-500 μM) stress. This CaGrx gene was overexpressed in Arabidopsis thaliana and investigated various biochemical and physiological performances under each metal stress. Transgenic plants showed significant up-regulation of the CaGrx gene during qRT-PCR analysis as well as longer roots, higher seed germination, and survival efficiency during each metal stress. The levels of stress markers, TBARS, H 2 O 2, and electrolyte leakage were found to be less in transgenic lines as compared to WT revealed less toxicity in transgenics. The total accumulation of AsIII, AsV, and Cr(VI) were significantly reduced in all transgenic lines except Cd, which was slightly reduced. The physiological parameters such as net photosynthetic rate (P N), stomatal conductance (g s), transpiration (E), water use efficiency (WUE), photochemical quenching (q P), and electron transport rate (ETR), were maintained in transgenic lines during metal stress. Various antioxidant enzymes such as glutaredoxin (GRX), glutathione reductase (GR), glutathione peroxidase (GPX), glutathione-S-transferase (GST), ascorbate peroxidase (APX), superoxide dismutase (SOD), catalase (CAT), dehydroascorbate reductase (DHAR), monodehydroascorbate reductase (MDHAR), antioxidant molecules (ascorbate, GSH) and stress-responsive amino acids (proline and cysteine) levels were significantly increased in transgenic lines which provide metal tolerance. The outcome of this study strongly indicates that the CaGrx gene participates in the moderation of metal stress in Arabidopsis, which can be utilized in biotechnological interventions to overcome heavy metal stress conditions in different crops. • CaGrx reduced metal accumulation in Arabidopsis under heavy metal stress. • CaGrx reduced the level of stress markers (TBARS, H 2 O 2, and electrolyte leakage). • CaGrx enhanced the level of antioxidant molecules, antioxidant enzymes, and stress-responsive amino acids. • CaGrx enhances the various physiological parameters against metal stress. • CaGrx protects the plant from oxidative damage. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Zn-Ag nanoparticle act as elicitor to synthesis secondary metabolites in W. somnifera.. • Nanoparticles increase photosynthesis and upregulates Calvin cycle genes. • Zn-Ag nanoparticles increase light absorption and oxidative stress. • Nanoparticles increase transcripts of withanolide biosynthesis and sterol content. • Quantum dots show increased ETR and did not impart withanolide biosynthesis. Abstract Withania somnifera is an important medicinal plant due to the presence of secondary metabolites. Nanoparticles (NPs) have elicitor activity for the enhancement of secondary metabolites biosynthesis in plants. W. somnifera plants were grown in-vitro and in-vivo and treated with homologous series of Zn-Ag NPs, Ni, and CdSe. Four NPs having different molar ratio of Zn and Ag have been used for the treatment. NP1, NP2, NP3, and NP4 Exhibit 19:1, 9:1, 3:1 and 1:1 molar ratios between Zn and Ag. Among all the treated NPs NP1 showed maximum enhancement in photosynthesis rate, transpiration rate, withanolide content and increase in some carbohydrates. Genes involved in photosynthesis, Calvin cycle, carbohydrate metabolism, and withanolide biosynthesis showed up regulation in NP1 and NP3 treatments. Zn-Ag NPs showed the photocatalytic and elicitor activity which helped in the light absorption and increased oxidative stress. NP2, NP4, Ni, and CdSe treatments showed the negative impact on withanolide biosynthesis and withanolide content. NP2, NP4, Ni, CdSe treated samples showed down regulation of most of the carbohydrate and withanolide pathway genes and lower withanolide content in comparison with water treated plants. CdSe caused excess cell damage, therefore, decrease in withanolide content was recorded. Gas exchange and electron transfer rate increased in CdSe and NP1 increases due to their semiconducting properties. CdSe and NP1 can liberate significant number of electrons under the light exposure, which behaves like carriers. Cyclic electron flux was observed in all the treatments but lowest in control condition. Cyclic electron flux not only manages the electron flow around PSI under stress but also considered as essential for photosynthesis and plant growth under control condition. [ABSTRACT FROM AUTHOR]

In general medicinal plants grown under water limiting conditions show much higher concentrations of secondary metabolites in comparison to control plants. In the present study, Withania somnifera plants were subjected to water stress and data related to drought tolerance phenomenon was collected and a putative mechanistic concept considering growth responses, physiological behaviour, and metabolite content and gene expression aspects is presented. Drought induced metabolic and physiological responses as well as drastic decrease in CO 2 uptake due to stomatal limitations. As a result, the consumption of reduction equivalents (NADPH 2+ ) for CO 2 assimilation via the calvin cycle declines significantly resulting in the generation of a large oxidative stress and an oversupply of antioxidant enzymes. Drought also results in the shifting of metabolic processes towards biosynthetic activities that consume reduction equivalents. Thus, biosynthesis of reduced compounds (isoprenoids, phenols and alkaloids) is enhanced. The dynamics of various metabolites have been discussed in the light of gene expression analysis of control and drought treated leaves. Gene encoding enzymes of pathways leading to glucose, fructose and fructan production, conversion of triose phosphates to hexoses and hexose phosphorylation were up-regulated in the drought stressed leaves. The down-regulated Calvin cycle genes were co-ordinately regulated with the down-regulation of chloroplast triosephosphate/phosphate translocator, cytoplasmic fructose-1,6-bisphosphate aldolase and fructose bisphosphatase. Expression of gene encoding Squalene Synthase (SQS) was highly upregulated under drought stress which is responsible for the diversion of carbon flux towards withanolides biosynthesis from isoprenoid pathway. [ABSTRACT FROM AUTHOR]

Drought is a major adverse environmental factor that limits plant productivity. Concomitant assimilation of carbon (C) and nitrogen (N) in illuminated leaves requires the regulated partitioning of reductant and photosynthate to sustain the demands of amino acid and carbohydrate biosynthesis. The short-term exposure to drought and its responses of photosynthesis and photosynthate partitioning to N enrichment was studied in Cyamopsis tetragonoloba (L.) Taub (guar). Four contrasting varieties of guar, HG-563, RGC-986 (drought-tolerant) and RGC-471, Varsha (drought-sensitive) were subjected to 15 days water stress and leaf tissues were studied in order to contemplate the counter strategy engaged under drought conditions. In guar plants, sensors trigger a signalling cascade that activates numerous proteins to induce the expression of certain genes involved in carbon and nitrogen metabolism.The levels of glucose, starch, and Glutamate dehydrogenase (GDH), Aspartate aminotransferase (AspAT), isocitrate dehydrogenase (ICDH), Nitrate Reductase (NR), and Nitrite reductase (NiR) activities were determined biochemically during 15 days drought treatment, at three stages. Further, the carbon (oxidative phosphorylation and TCA cycle) - nitrogen metabolic pathway interaction was studied at the molecular level. The respiratory pathway genes were upregulated, while the nitrogen metabolic pathway genes were downregulated under all stages of drought in guar plants. The physiological, biochemical and molecular data suggests that the high rates of dark respiration was insufficient to provide extra carbon required to assist amino acid synthesis but rather sufficed by a rapid metamorphosis in the photosynthetic carbon partitioning to amino acid metabolism via the nitrogen metabolism. [Display omitted] • Drought causes NADH DEHYDROGENASE gene to escalate dark respiration. • Nitrogen assimilation reduces under drought in leguminous Cyamopsis tetragonoloba. • Drought triggers protein kinase cascade signalling in guar plants. • Drought regulates nitrogen metabolic genes in guar. • Drought triggers increase in sugar content at the cost of amino acids. [ABSTRACT FROM AUTHOR]