Photosynthetic activity and RAPD profile of polyethylene glycol treated B. juncea L. under nitric oxide and abscisic acid application

Role of phenylpropanoid pathway in genetic regulation and physiological adaptation in arsenic stressed rice genotypes

This study investigates the role of the phenylpropanoid pathway in arsenic (As) contaminated rice genotypes under natural conditions, exploring the intricate relationship between genetic regulation and physiological adaptation. Differential approaches adapted by rice genotypes to counteract As exposure are elucidated here through analysis of enzyme activities and related gene expression patterns, docking simulations, and nutrient dynamics. Enzymatic analysis from the phenylpropanoid pathway revealed significant variations across rice genotypes, with Mini mansoori exhibiting notably higher activity levels of key enzymes (PAL, C4H, 4CL, CHI, DFR and F3H) compared to Sampoorna and Pioneer. Additionally, the gene expression profiling unveiled differential responses, with Mini mansoori and Pioneer demonstrating higher expression of genes (OsPAL, OsCHS, OsCHI, OsF3H, OsF3'H, OsFLS, OsDFR, and OsLAR) associated with As resistance and tolerance, compared to Sampoorna. Enrichment analysis emphasized the involvement of cinnamic acid biosynthesis and related pathways. Molecular docking depicted certain proteins, such as Os4CL, OsFLS, OsDFR, and OsLAR susceptible to As binding, potentially affecting enzymatic activity. Ionomic analysis unveiled that Mini mansoori maintained higher levels of essential nutrients such as Na, Ca, P, Mn, Mg, and Zn in grains. However, this contrasted with Pioneer and Sampoorna, which experienced nutrient imbalance likely due to higher As accumulation. Chlorophyll fluorescence analysis depicted that Mini mansoori and Pioneer maintained better photosynthetic efficiency under As toxicity compared to Sampoorna. Moreover, network analysis highlights the critical role of Mg and Na interaction with essential phenolics and flavonoids, in combating the stress. Harnessing this understanding, targeted breeding effort could yield As-resistant rice varieties with enhanced nutrient and flavonoid contents, addressing both food safety and malnutrition in affected regions.

Different techniques reveal the difference of community structure and function of fungi from root and rhizosphere of Salvia miltiorrhiza Bunge

Fungi have essential functions in plant health and performance. However, the plant-associated functions of many cultured fungi have not been established in detail. Here, the fungal species diversity in Salvia miltiorrhiza roots and rhizosphere was assessed for the first time using culturomics and high-throughput sequencing. We present a comprehensive functional metagenomic analysis of these fungi and verified activity of cellulase and chitinase predicted in the metagenomic analysis. We first collected and cultured fungi from the root and rhizosphere of S. miltiorrhiza. We found 92 species across 37 families and five phyla, with Ascomycota being dominant. Many rDNA internal transcribed spacer sequences could not be assigned to lower taxonomic levels. There were 19 genera of endophytic fungi and 37 genera of rhizosphere fungi. The culturomics approach had lower taxonomic diversity than high-throughput sequencing, but some fungi were only found in cultures. Structural analyses indicated that the dominant species differed in cultured and non-cultured samples at other levels, apart from the phylum level. Functional analysis mapped 223 carbohydrate enzyme families and 393 pathways in the CAZy and KEGG databases, respectively. The most abundant families were glycoside hydrolases and those involved in carbohydrate metabolism. As predicted by metagenomics, we experimentally verified cellulase and chitinase activity for 29 and 74 fungi, respectively. We provide the first evidence of biomass recycling by fungi that are associated with plants. Culturing is essential to reveal the hidden microbial community and critical functions in plant-microbe interactions.

Iono-metabolomic guided elucidation of arsenic induced physiological and metabolic dynamics in wheat genotypes

Despite the growing concerns about arsenic (As) toxicity, information on wheat adaptability in such an aggravating environment is limited. Thus, the present investigation based on an iono-metabolomic approach is aimed to decipher the response of wheat genotypes towards As toxicity. Wheat genotypes procured from natural conditions were characterized as high As-contaminated (Shri ram-303 and HD-2967) and low As-contaminated (Malviya-234 and DBW-17) based on ICP-MS As accumulation analysis. Reduced chlorophyll fluorescence attributes, grain yield and quality traits, and low grain nutrient status were accompanied by remarkable grain As accumulation in high As-contaminated genotypes, thus imposing a higher potential cancer risk and hazard quotient. Contrarily, in low As-contaminated genotypes, the richness of Zn, N, Fe, Mn, Na, K, Mg, and Ca could probably have supported less grain As accumulation, imparting better agronomic and grain quality traits. Additionally, from metabolomic analysis (LC-MS/MS and UHPLC), abundances of alanine, aspartate, glutamate, quercetin, isoliquiritigenin, trans-ferrulic, cinnamic, caffeic, and syringic bestow Malviya-234 as the best edible wheat genotype. Further, the multivariate statistical analysis (HCA, PCA, and PLS-DA) revealed certain other key metabolites (rutin, nobletin, myricetin, catechin, and naringenin) based genotypic discrimination that imparts strength to genotypes for better adaptation in harsh conditions. Out of the 5 metabolic pathways ascertained through topological analysis, the two main pathways vital for plant's metabolic adjustments in an As-induced environment were: 1. The alanine, aspartate and glutamate metabolism pathway, and 2. The flavonoid biosynthesis pathway. This is also evident from network analysis, which stipulates amino acid metabolism as a prominent As regulatory factor closely associated with flavonoids and phenolics. Therefore, the present findings are useful for wheat breeding programs to develop As adaptive genotypes that are beneficial for crop improvement and human health.

Multiple Ways of Nitric Oxide Production in Plants and Its Functional Activity under Abiotic Stress Conditions

Nitric oxide (NO) is an endogenous signaling molecule that plays an important role in plant ontogenesis and responses to different stresses. The most widespread abiotic stress factors limiting significantly plant growth and crop yield are drought, salinity, hypo-, hyperthermia, and an excess of heavy metal (HM) ions. Data on the accumulation of endogenous NO under stress factors and on the alleviation of their negative effects under exogenous NO treatments indicate the perspectives of its practical application to improve stress resistance and plant productivity. This requires fundamental knowledge of the NO metabolism and the mechanisms of its biological action in plants. NO generation occurs in plants by two main alternative mechanisms: oxidative or reductive, in spontaneous or enzymatic reactions. NO participates in plant development by controlling the processes of seed germination, vegetative growth, morphogenesis, flower transition, fruit ripening, and senescence. Under stressful conditions, NO contributes to antioxidant protection, osmotic adjustment, normalization of water balance, regulation of cellular ion homeostasis, maintenance of photosynthetic reactions, and growth processes of plants. NO can exert regulative action by inducing posttranslational modifications (PTMs) of proteins changing the activity of different enzymes or transcriptional factors, modulating the expression of huge amounts of genes, including those related to stress tolerance. This review summarizes the current data concerning molecular mechanisms of NO production and its activity in plants during regulation of their life cycle and adaptation to drought, salinity, temperature stress, and HM ions.

Abscisic Acid May Play a Critical Role in the Moderating Effect of Epichloë Endophyte on Achnatherum inebrians under Drought Stress

Water scarcity is a major constraint that adversely affects plant development and growth. Abscisic acid (ABA) is a plant stress hormone that is rapidly synthesized and can induce stomatal closure to conserve water, thereby alleviating the drought stress of plants. The Epichloë endophyte enhances the drought tolerance of Achnatherum inebrians (drunken horse grass, DHG). To better understand how the Epichloë endophyte enhances drought tolerance, DHG plants without (EF) and with (EI), an Epichloë endophyte, were grown under 20% and 60% soil water conditions (SWC), and the leaves of the three treatments of EF and EI plants were sprayed with ABA solution (1 mg/L); fluridone (FLU), the ABA biosynthesis inhibitor solution (1 mg/L); and distilled water, respectively. Four-weeks later, the results indicated that the exogenous ABA application promoted plant growth, stomatal conductance, and photosynthetic rate, while the opposite effect occurred with plants sprayed with FLU. The differences between EI and EF plants in tiller number, height, chlorophyll content, stomata conductance, and photosynthetic rate were highest when sprayed with ABA. Thus, it is concluded that ABA might be involved in the moderating effect of Epichloë endophytes on DHG plants exposed to drought by maintaining growth and improving photosynthetic efficiency.

Nitric oxide mediated alleviation of abiotic challenges in plants

Agriculture and ecosystem are negatively influenced by the abiotic stresses which create solemn pressures on plants as they are sessile in nature leading to excessive losses in economy. For maintenance of sustainable agriculture and to fulfil the cumulative call of food for rapidly growing population worldwide, it becomes crucial to protects the crop plants from climate fluctuations. Plants fight back against these challenges by generation of redox molecules comprising reactive oxygen species (ROS) and reactive nitrogen species (RNS) and cause modulation at cellular, physiological and molecular levels. Nitric oxide (NO) deliver tolerance to several biotic and abiotic stresses in plants by acting as signalling molecule or free radicals. It is also intricated in several developmental processes in plants using different mechanisms. Supplementation of exogenous NO reduce toxicity of abiotic stresses and provide resistance. In this review article, we summarize the recent research studies (five years) depicting the functional role of NO in alleviation of abiotic stresses such as drought, cold, heat, heavy metals and flooding. Moreover, by investigating studies found that among heavy metals works associated with Hg, Pb, and Cr is limited comparatively. Additionally, role of NO in abiotic stress resistance such as cold, freezing and heat stress less/poorly investigated. Consequently, further emphasis should be diverted towards how NO can facilitate protection against these stresses. In recent studies mostly beneficial role of NO against abiotic challenges have been elucidated by observing physiological/biochemical parameters but relatively inadequate research done at the transcripts level or gene regulation subsequently researchers should include it in future. Lastly, brief outline and an evaluative discussion on the present information and future prospective provided. Altogether, these inclusive experimental agendas could facilitate in future to produce climate tolerant plants. This will help to confront the constant fluctuations in the environment and to reduce the challenges in way of agriculture productivity and global food demands.

Root NRT, NiR, AMT, GS, GOGAT and GDH expression levels reveal NO and ABA mediated drought tolerance in Brassica juncea L

Little is known about the interactive effects of exogenous nitric oxide (NO) and abscisic acid (ABA) on nitrogen (N) metabolism and related changes at molecular and biochemical levels under drought stress. The present study highlights the independent and combined effect of NO and ABA (grouped as "nitrate agonists") on expression profiles of representative key genes known to be involved in N-uptake and assimilation, together with proline metabolism, N-NO metabolism enzyme's activity and nutrient content in polyethylene glycol (PEG) treated roots of Indian mustard (B. juncea cv. Varuna). Here we report that PEG mediated drought stress negatively inhibited growth performance, as manifested by reduced biomass (fresh and dry weight) production. Total N content and other nitrogenous compounds (NO3-, NO2-) were decreased; however, NH4+, NH4+/ NO3- ratio and total free amino acids content were increased. These results were positively correlated with the PEG induced changes in expression of genes and enzymes involved in N-uptake and assimilation. Also, PEG supply lowered the content of macro- and micro-nutrients but proline level and the activity of ∆1-pyrroline-5-carboxylate synthetase increased indicating increased oxidative stress. However, all these responses were reversed upon the exogenous application of nitrate agonists (PEG + NO, PEG + NO + ABA, and PEG + ABA) where NO containing nitrate agonist treatment i.e. PEG + NO was significantly more effective than PEG + ABA in alleviating drought stress. Further, increases in activities of L-arginine dependent NOS-like enzyme and S-nitrosoglutathione reductase were observed under nitrate agonist treatments. This indicates that the balanced endogenous change in NO and ABA levels together during synthesis and degradation of NO mitigated the oxidative stress in Indian mustard seedlings. Overall, our results reveal that NO independently or together with ABA may contribute to improved crop growth and productivity under drought stress.

Plant Nitric Oxide Signaling under Drought Stress

Water deficit caused by drought is a significant threat to crop growth and production. Nitric oxide (NO), a water- and lipid-soluble free radical, plays an important role in cytoprotection. Apart from a few studies supporting the role of NO in drought responses, little is known about this pivotal molecular amendment in the regulation of abiotic stress signaling. In this review, we highlight the knowledge gaps in NO roles under drought stress and the technical challenges underlying NO detection and measurements, and we provide recommendations regarding potential avenues for future investigation. The modulation of NO production to alleviate abiotic stress disturbances in higher plants highlights the potential of genetic manipulation to influence NO metabolism as a tool with which plant fitness can be improved under adverse growth conditions.