Ravdeep Kaur

Redox homeostasis in plants under abiotic stress: role of electron carriers, energy metabolism mediators and proteinaceous thiols

Contemporaneous presence of both oxidized and reduced forms of electron carriers is mandatory in efficient flux by plant electron transport cascades. This requirement is considered as redox poising that involves the movement of electron from multiple sites in respiratory and photosynthetic electron transport chains to molecular oxygen. This flux triggers the formation of superoxide, consequently give rise to other reactive oxygen species (ROS) under adverse environmental conditions like drought, high or low temperature, heavy metal stress etc. that plants owing during their life span. Plant cells synthesize ascorbate, an additional hydrophilic redox buffer, which protect the plants against oxidative challenge. Large pools of antioxidants also preside over the redox homeostasis. Besides, tocopherol is a liposoluble redox buffer, which efficiently scavenges the ROS like singlet oxygen. In addition, proteinaceous thiol members such as thioredoxin, peroxiredoxin and glutaredoxin, electron carriers and energy metabolism mediators phosphorylated (NADP) and non-phosphorylated (NAD+) coenzyme forms interact with ROS, metabolize and maintain redox homeostasis.

Role of various hormones in photosynthetic responses of green plants under environmental stresses.

Environmental stress includes adverse factors like water deficit, high salinity, enhanced temperature and heavy metals etc. These stresses alter the normal growth and metabolic processes of plants including photosynthesis. Major photosynthetic responses under various stresses include inhibition of photosystems (I and II), changes in thylakoid complexes, decreased photosynthetic activity and modifications in structure and functions of chloroplasts etc. Various defense mechanisms are triggered inside the plants in response to these stresses that are regulated by plant hormones or plant growth regulators. These phytohormones include abscisic acid, auxins, cytokinins, ethylene, brassinosteroids, jasmonates and salicylic acid etc. The present review focuses on stress protective effects of plants hormones on the photosynthetic responses.

Differential distribution of amino acids in plants

Plants are a rich source of amino acids and their individual abundance in plants is of great significance especially in terms of food. Therefore, it is of utmost necessity to create a database of the relative amino acid contents in plants as reported in literature. Since in most of the cases complete analysis of profiles of amino acids in plants was not reported, the units used and the methods applied and the plant parts used were different, amino acid contents were converted into relative units with respect to lysine for statistical analysis. The most abundant amino acids in plants are glutamic acid and aspartic acid. Pearson’s correlation analysis among different amino acids showed that there were no negative correlations between the amino acids. Cluster analysis (CA) applied to relative amino acid contents of different families. Alismataceae, Cyperaceae, Capparaceae and Cactaceae families had close proximity with each other on the basis of their relative amino acid contents. First three components of principal component analysis (PCA) explained 79.5% of the total variance. Factor analysis (FA) explained four main underlying factors for amino acid analysis. Factor-1 accounted for 29.4% of the total variance and had maximum loadings on glycine, isoleucine, leucine, threonine and valine. Factor-2 explained 25.8% of the total variance and had maximum loadings on alanine, aspartic acid, serine and tyrosine. 14.2% of the total variance was explained by factor-3 and had maximum loadings on arginine and histidine. Factor-4 accounted 8.3% of the total variance and had maximum loading on the proline amino acid. The relative content of different amino acids presented in this paper is alanine (1.4), arginine (1.8), asparagine (0.7), aspartic acid (2.4), cysteine (0.5), glutamic acid (2.8), glutamine (0.6), glycine (1.0), histidine (0.5), isoleucine (0.9), leucine (1.7), lysine (1.0), methionine (0.4), phenylalanine (0.9), proline (1.1), serine (1.0), threonine (1.0), tryptophan (0.3), tyrosine (0.7) and valine (1.2).

Castasterone confers copper stress tolerance by regulating antioxidant enzyme responses, antioxidants, and amino acid balance in B. juncea seedlings

The aim of the present study was to explore the effect of exogenous application of castasterone (CS) on physiologic and biochemical responses in Brassica juncea seedlings under copper (Cu) stress. Seeds were pre-soaked in different concentrations of CS and grown for 7 days under various levels of Cu. The exposure of B. juncea to higher levels of Cu led to decrease of morphologic parameters, with partial recovery of length and fresh weight in the CS pre-treated seedlings. Metal content was high in both roots and shoots under Cu exposure while the CS pre-treatment reduced the metal uptake. Accumulation of hydrogen peroxide (H2O2) and superoxide anion radical (O2-) were chosen as stress biomarker and higher levels of H2O2 (88.89%) and O2- (62.11%) showed the oxidative stress in metal treated B. juncea seedlings, however, CS pre-treatment reduced ROS accumulation in Cu-exposed seedlings. The Cu exposures lead to enhance the plants enzymatic and non-enzymatic antioxidant system. It was observed that enzymatic activities of ascorbate peroxidase (APOX), dehydroascorbate reductase (DHAR), and glutathione reductase (GR), glutathione perxoidase (GPOX) and gultrathione-s-transferase increased while activity of monodehydroascorbate reductase (MDHAR) decreased under Cu stress. The pre-treatment with CS positively affected the activities of enzymes. RT-PCR analysis showed that mRNA transcript levels were correlated with total enzymatic activity of DHAR, GR, GST and GSH. Increase in the gene expression of DHAR (1.85 folds), GR (3.24 folds), GST-1 (2.00 folds) and GSH-S (3.18 folds) was noticed with CS pre-treatment. Overall, the present study shows that Cu exposure induced severe oxidative stress in B. juncea plants and exogenous application of CS improved antioxidative defense system by modulating the ascorbate-glutathione cycle and amino acid metabolism.

Castasterone assisted accumulation of polyphenols and antioxidant to increase tolerance of B. juncea plants towards copper toxicity

Abstract The concentration of copper in soil is increasing, which may potentially affect the crop yield. Brassinosteroids are well known to enhance tolerance towards abiotic stress, but role of castasterone in this context is poorly understood. The present study was designed to explore the potential of castasterone to enhance copper tolerance in Brassica juncea plants. Results indicate that copper increased the production of superoxide anion radical and hydrogen peroxide, maximum at 0.75 mM of copper exposure (31.71 and 68.29% at 60 days). This overproduction of reactive oxygen species hampered the photosynthetic pigments and gas exchange parameters. Application of castasterone as seed soaking method significantly activated the enzymatic defense system. Superoxide dismutase, polyphenol oxidase and catalase showed maximum enhancement in the activities. The study further highlighted the modulations of polyphenols in B. juncea with castasterone and copper. Phenolic profiling shows that accumulation of polyphenols increase with the castasterone application under copper stress. Caffeic acid, ellagic acid, catechin and chlorogenic acid were the most prominent polyphenols observed in this study.

Modulation of antioxidative defense expression and osmolyte content by co-application of 24-epibrassinolide and salicylic acid in Pb exposed Indian mustard plants

The study focuses on potential of combined pre-soaking treatment of 24-Epibrassinolide (EBL) and Salicylic acid (SA) in alleviating Pb phytotoxicity in Brassica juncea L. plants. The seeds after treatment with combination of both the hormones were sown in mixture of soil, sand and manure (3:1:1) and were exposed to Pb concentrations (0.25mM, 0.50mM and 0.75mM). After 30 days of growth, the plants were harvested and processed, for quantification of various metabolites. It was found that pre-sowing of seeds in combination of EBL and SA, mitigated the adverse effects of metal stress by modulating antioxidative defense response and enhanced osmolyte contents. Dry matter content and heavy metal tolerance index were enhanced in response to co-application of EBL and SA. The levels of superoxide anions, hydrogen peroxide and malondialdehyde were lowered by the combined treatment of hormones. Enhancement in activities of guaiacol peroxidase, catalase, glutathione reductase and glutathione-s-transferase were recorded. Contents of glutathione, tocopherol and ascorbic acid were also enhanced in response to co-application of both hormones. Expression of POD, CAT, GR and GST1 genes were up-regulated whereas SOD gene was observed to be down-regulated. Contents of proline, trehalose and glycine betaine were also reported to be elevated as a result of treatment with EBL+SA. The results suggest that co-application of EBL+SA may play an imperative role in improving the antioxidative defense expression of B. juncea plants to combat the oxidative stress generated by Pb toxicity.

ROS Compartmentalization in Plant Cells Under Abiotic Stress Condition

Reactive oxygen species (ROS) are generated in various plant organelles under normal conditions and play an important role in different physiological progressions. But under abiotic stress, excessive ROS generation takes place which causes damage to normal functioning of plants. ROS play a dual role as they cause cellular damage and are also involved in abiotic stress signaling. Therefore, it is important to investigate the features of appearance of physiological effects of ROS depending on their cellular localization under the abiotic stress. Plants possess certain antioxidative mechanisms to deal with excess ROS in the cells, which involves enzymatic and nonenzymatic antioxidants. In the review, the mechanisms of ROS formation in different cellular compartments like mitochondria, peroxisomes, chloroplasts, nucleus, vacuole, cell wall, and plasma membranes are considered and summarized.

Chapter 19 – Prospects of Field Crops for Phytoremediation of Contaminants

Anthropogenic activities have led to increased pollution of soil all over the world. These pollutants can be either organic (e.g., PCBs, PAHs, fertilizers, pesticides) or inorganic pollutants including various heavy metals (e.g., Cd, Cu, As, Zn, Hg, Pb). Phytoremediation is a green technology in which plants are used to clean up pollutants from water and soil. This environmentally friendly and cost-effective technology is now focusing on higher plants with large biomass that have a high tolerance to pollutants. Due to low shoot and root growth of hyperaccumulator plants, phytoremediation study has moved toward the high biomass species such as herbaceous field crops. Field crops may have low metal concentrations, but they compensate this with their high biomass yield. Various amendments, such as use of chelating agents, plant growth-promoting bacteria, plant growth-promoting hormones, and mycorrhizae, can be used to increase the phytoremediation potential of field crops. Molecular techniques used to produce transgenic plants also show promise for the efficient use of field crops for phytoremediation. Thus, due to the higher growth potential of field crops compared to hyperaccumulators, phytoremediation efficiency should be thought of as a future significant remediation tool.

Brassinosteroids: Improving Crop Productivity and Abiotic Stress Tolerance

Brassinosteroids (BRs), a group of phyto-steroidal hormones, play crucial role in a wide spectrum of biochemical, physiological, growth, and developmental processes in plants. Recent molecular and physiological studies have further revealed the efficacy of BRs in improving the crop yield and productivity by controlling several genes regulated at cellular and sub-cellular levels. BRs also regulate several important agronomic traits like rhizogenesis, senescence, abscission, flower and fruit development, fruit ripening, flower sex expression, yield and quality of seed, grain, and fiber in horticultural and cash crops. These eco-friendly, nontoxic, and biosafe steroidal phytohormones when applied at specific dose at specific stage of development of specific crop enhanced quantity and quality of field-grown crops. Moreover, BRs also possess anti-ecdysteroidal, antiviral, and antifungal properties, and thus are considered as potential substitute to conventional pesticide, insecticide, and herbicide. Therefore, the present book chapter will update the knowledge of BRs in improving crop yield by ameliorating abiotic stresses such as salinity, drought, extreme temperatures, heavy metals, and pesticides. Besides, the current research has highlighted BRs-mediated cell elongation in vegetative organs as well as meristem homeostasis in plants. Various studies on BRs-related mutants indicated that steady BRs signaling is required for the optimal root growth, which further emphasized the indispensable roles of BRs in the regulation of the cell-cycle progression and differentiation in plants. Furthermore, the current chapter focuses on the exogenous application of effective doses of BRs to stress-affected plants as better and simple alternative approach for protecting plants from environmental stresses in comparison to the regular plant breeding practices.

Potential of Endophytic Bacteria in Heavy Metal and Pesticide Detoxification

Heavy metal (HM) and pesticide contamination in the soil is of major concern in the present era. Both of these contaminants disturb soil microflora and adversely affect the growth and development of plants. The soil contamination can be reduced by ecofriendly techniques. The use of endophytic bacteria (EB) in the rhizosphere is one such technique where EB reduce the HM and pesticide contaminants in the soil. They can efficiently reduce the HM and pesticide concentration in the soil by enhancing the phytoremediating efficiency of plants. Moreover, EB can also degrade the pesticides in soil by producing various hormones and enzymes which ultimately result in promotion of the growth of plants. Hence, keeping in mind the efficiency of EB in reducing the HM and pesticide contamination in soil, the present review gives a detailed view of HM and pesticide detoxification by these bacteria.