Ruby Chandna

Role of Glutathione Reductase in Plant Abiotic Stress

Abiotic stresses severely affect the growth, development, and ultimately yield of the plant, which results in heavy economic losses and food crisis. Oxidative stress, which is associated with almost all the abiotic stresses, is due to over production of toxic reactive oxygen species (ROS) including superoxide ion, hydrogen peroxide, and hydroxyl radicals. Plants combat the oxidative stress via enzymatic and non-enzymatic machinery. Glutathione reductase (GR) is one of the potential enzymes of the enzymatic antioxidant system, which sustains the reduced status of GSH via Ascorbate–Glutathione pathway and plays a vital role in maintenance of sulfhydryl (–SH) group and acts as a substrate for glutathione-S-transferases. GR has been characterised and has been used in the transgenics to provide the plants with tolerance against the oxidative stress.

Potassium starvation-induced oxidative stress and antioxidant defense responses in Brassica juncea

In this study, changes in growth, chlorophyll pigments, proline, hydrogen peroxide (H2O2) and malondialdehyde (MDA) contents, and antioxidative enzyme activities were investigated in the seedlings of four different cultivars (cvs) of mustard [Brassica juncea (L.) Czern. & Coss.], i.e. Varuna, RH-30, Rohini, and Vaibhave under potassium (K) nutrition-deficient conditions. K deficiency induced a significant decrease in concentrations of photosynthetic pigments in all four cvs, however, this decrease was higher in cvs. Varuna and RH-30. During K deficiency, proline concentration increased in all mustard cvs, but a maximum increase in this parameter was shown by cvs. Varuna and RH-30. The activity of the key proline metabolizing enzyme γ-glutamyl kinase increased more in cvs. Varuna and RH-30 compared to cvs. Rohini and Vaibhave. The proline oxidase activity showed greater increase in cvs. Vaibhave and Rohini compared to cvs. Varuna and RH-30. K deficiency increased the concentrations of H2O2 and the activities of anti-oxidative defense system enzymes like superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), and glutathione reductase (GR) in the seedlings of all mustard cvs, but higher activities of these enzymes were observed in cvs. Varuna and RH-30 compared to cvs. Rohini and Vaibhave. A significant lipid peroxidation in terms of MDA contents was also observed in the K-deficient seedlings of all four mustard cvs. This study suggests that K-starvation-induced oxidative stress through the high generation of reactive oxygen species (ROS). All mustard cvs counteracted to some extent the effects of ROS by activation of antioxidant machinery. Overall, the results indicate that of all four mustard cvs, Varuna and RH-30 were tolerant to K deficiency.

Relevance of Proteomic Investigations in Plant Abiotic Stress Physiology

Plant growth and productivity are influenced by various abiotic stresses. Stressful conditions may lead to delays in seed germination, reduced seedling growth, and decreased crop yields. Plants respond to environmental stresses via differential expression of a subset of genes, which results in changes in omic compositions, such as transcriptome, proteome, and metabolome. Since the development of modern biotechnology, various research projects have been carried out to understand the approaches that plants have adopted to overcome environmental stresses. Advancements in omics have made functional genomics easy to understand. Since the fundamentals of classical genomics were unable to clear up confusion related to the functional aspects of the metabolic processes taking place during stress conditions, new fields have been designed and are known as omics. Proteomics, the analysis of genomic complements of proteins, has caused a flurry of activity in the past few years. It defines protein functions in cells and explains how those protein functions respond to changing environmental conditions. The ability of crop plants to cope up with the variety of environmental stresses depends on a number of changes in their proteins, which may be up- and downregulated as a result of altered gene expression. Most of these molecules display an essential function, either in the regulation of the response (e.g., components of the signal transduction pathway), or in the adaptation process (e.g., enzymes involved in stress repair and degradation of damaged cellular contents), allowing plants to recover and survive the stress. Many of these proteins are constitutively expressed under normal conditions, but when under stress, they undergo a modification of their expression levels. This review will explain how proteomics can help in elucidating important plant processes in response to various abiotic stresses.

Enhancing Plant Productivity Under Salt Stress: Relevance of Poly-omics

At present more than 20% of all the irrigated land in the world is estimated as affected by salinity and this trend is increasing with the rapid climate changes as well as the excess use of irrigation water. Salt stress is one of the most devastating abiotic stresses which severely affects the agricultural productivity in various ways. High concentration of salt in the soil or in the irrigation water can have a overwhelming effect on plant metabolism, disrupting cellular homeostasis and uncoupling major physiological and biochemical processes. Salinity cause both osmotic stress and ionic toxicity which hamper the plant productivity by inhibiting or altering the plant growth, dry matter partitioning, seed germination, photosynthesis and yield. Considering the devastating effect of salt stress on plants, one of the important tasks for plant biologists is to explore the approaches that are able to develop salt tolerance in crop plants. In fact, salt tolerance is a multigenic trait which is governed by various morphological and physiological factors. Thus omics approaches therefore, come in forefront to develop salt tolerance as a part of different strategies of conventional plant breeding. Transcriptomics, proteomics, metabolomics, ionomics and micromics together have been a bloom in revealing plant stress responses and the mechanisms that underlie these responses. These techniques have been playing important part in discovering new genes, proteins and secondary plant metabolites those are responsible for plants adaptation to stress. In this review, we have focused on the causes and effects of salinity on crop plants and possible mechanisms of salt tolerance including the possible use of omics in conferring salt tolerance.

Variability in Indian bread wheat (Triticum aestivum L.) varieties differing in nitrogen efficiency as assessed by microsatellite markers

Wheat (Triticum aestivum L.) is a staple food for half of the world. Its productivity and agronomical practices, especially for nitrogen supplementation, is governed by the nitrogen efficiency (NE) of the genotypes. We analyzed 16 popular cultivated Indian varieties of wheat for their NE and variability estimates using a set of 21 simple sequence repeat (SSR) markers, derived from each wheat chromosome. These genotypes were categorized into three groups, viz., low, moderate, and high nitrogen efficient. Of these 16 genotypes, we have reported six, eight, and two genotypes in high, moderate, and low NE categories, respectively. The differential NE in these genotypes was supported by nitrogen uptake and assimilation parameters. The values of average polymorphic information content and marker index for these SSR markers were estimated to be 0.32 and 0.59, respectively. The genetic similarity coefficient for all possible pairs of varieties ranged from 0.41 to 0.76, indicating the presence of considerable range of genetic diversity at molecular level. The dendrogram prepared on the basis of unweighted pair-group method of arithmetic average algorithm grouped the 16 wheat varieties into three major clusters. The clustering was strongly supported by high bootstrap values. The distribution of the varieties in different clusters and subclusters appeared to be related to their variability in NE parameter that was scored. Genetically diverse parents were identified that could potentially be used for their desirable characteristics in breeding programs for improvement of NE in wheat.

Physiological and Molecular Analysis of Applied Nitrogen in Rice Genotypes

Ten genotypes of rice (Oryza sativa L.) were grown for 30 d in complete nutrient solution with 1 mmol/L (N-insufficient), 4 mmol/L (N-moderate) and 10 mmol/L (N-high) nitrogen levels, and nitrogen efficiency (NE) was analyzed. Growth performance, measured in terms of fresh weight, dry weight and lengths of root and shoot, was higher in N-efficient than in N-inefficient rice genotypes at low N level. Of these 10 genotypes, Suraksha was identified as the most N-efficient, while Vivek Dhan the most N-inefficient. To find out the physiological basis of this difference, the nitrate uptake rate of root and the activities of nitrate assimilatory enzymes in leaves of N-efficient and N-inefficient rice genotypes were studied. Uptake experiments revealed the presence of two separate nitrate transporter systems mediating high- and low-affinity nitrate uptake. Interestingly, the nitrate uptake by the roots of Suraksha is mediated by both high- and low-affinity nitrate transporter systems, while that of Vivek Dhan by only low-affinity nitrate transporter system. Study of the activities and expression levels of nitrate assimilatory enzymes in N-efficient and N-inefficient rice genotypes showed that nitrate reductase (NR) and glutamine synthetase (GS) play important roles in N assimilation under low-nitrogen conditions.

Recent Advances of Metabolomics to Reveal Plant Response During Salt Stress

Salt stress is the major limiting factor in agriculture and portraits a major challenge to food security. The adverse effect of salt stress is expressed on whole plant levels. Plants have acquired various processes that functions to balance cellular hyperosmolarity and ion disequilibrium in an effort to combat salt stress. These processes occur due to significant changes in the gene expression that in turn bring about changes in plant metabolism. These metabolic changes help the plant to adapt to disorganized metabolic homeostasis. It has been observed that adverse growth conditions have impact on the synthesis of secondary plant products or metabolites that help in plant defence. The diverse nature of these metabolites has lead to the development of ‘Metabolomics’. The metabolite fingerprinting and profiling approaches provides accurate identification and quantification of stressed sample even before they can bring about change(s) in the transcriptome or proteome. Using metabolic profile changes as a marker for stress physiology, metabolic movements and factors can be analysed in combination with other ‘omic’ techniques, such as transcriptomics. Revealed analyses of salt acclimation effects and related stress factors to salinity stress may provide help in crop breeding programs to develop salt tolerance varieties. In this review, we will focus on recent advancements and application of metabolomics in plants under salinity stress.

Differential response of wheat genotypes to applied nitrogen: biochemical and molecular analysis

Nitrogen-efficient and nitrogen-inefficient wheat genotypes were identified on the basis of the differential response of 16 wheat genotypes with low (1 mM) and high (25 mM) nitrogen (N) supply. Growth performance, measured in terms of fresh weight, dry weight and length of root and shoot, was higher in N-efficient than N-inefficient wheat genotypes at low N levels. Interestingly, although the growth of N-efficient genotypes did not show any change with increasing level of N supply, there was a marked increase in the growth of N-inefficient genotypes with the increase in N level. To work out the basis of this differential response of wheat genotypes to low N levels, we investigated the nitrate uptake rate of root and activities of nitrate assimilatory enzymes in the leaves of N-efficient and N-inefficient wheat genotypes. Nitrate uptake kinetics of these genotypes revealed that the uptake of nitrate in N-efficient genotypes was mediated by high-affinity nitrate transporter systems, whereas those of N-inefficient genotypes was mediated by low-affinity nitrate transporter systems. Study of the activities and expression levels of nitrate assimilatory enzymes in N-efficient and N-inefficient wheat genotypes showed that nitrate reductase (NR) and glutamine synthetase (GS) play important roles in N assimilation under low-nitrogen conditions.

Nitrogen stress-induced alterations in the leaf proteome of two wheat varieties grown at different nitrogen levels

Inorganic nitrogen (N) is a key limiting factor of the agricultural productivity. Nitrogen utilization efficiency has significant impact on crop growth and yield as well as on the reduction in production cost. The excessive nitrogen application is accompanied with severe negative impact on environment. Thus to reduce the environmental contamination, improving NUE is need of an hour. In our study we have deployed comparative proteome analysis using 2-DE to investigate the effect of the nitrogen nutrition on differential expression pattern of leaf proteins in low-N sensitive and low-N tolerant wheat (Triticum aestivum L.) varieties. Results showed a comprehensive picture of the post-transcriptional response to different nitrogen regimes administered which would be expected to serve as a basic platform for further characterization of gene function and regulation. We detected proteins related to photosynthesis, glycolysis, nitrogen metabolism, sulphur metabolism and defence. Our results provide new insights towards the altered protein pattern in response to N stress. Through this study we suggest that genes functioning in many physiological events coordinate the response to availability of nitrogen and also for the improvement of NUE of crops.

Proteomic Markers for Oxidative Stress: New Tools for Reactive Oxygen Species and Photosynthesis Research

Abiotic stresses are the primary causes of crop loss worldwide. Photosynthesis is an important phenomenon that is particularly affected towards reactive oxygen species, generated during any stress condition in an organism. Oxidative stresses in plants leads to debilitation and death or to response and tolerance. The sub-cellular energy organelles (chloroplast, mitochondria and peroxisomes), responsible for major metabolic processes including photosynthesis, photorespiration, oxidative phosphorylation, β-oxidation and the tricarboxylic acid cycle, are much affecting centers in a plant cell by oxidative stresses. Plant adaptation to environmental stresses is dependent upon the activation of cascades of molecular networks involved in stress perception, signal transduction, and the expression of specific stress related genes and metabolites. Progress in genomics, proteomics and metabolomics results in more understanding of global cellular responses to oxidative stress on transcript, protein, and metabolite levels. Elucidating the function of proteins expressed by genes in stress tolerant and susceptible plants would advance our understanding of plant adaptation and tolerance to environmental stresses, but also may provide important information for designing new strategies for crop improvement.