Sukhmeen Kaur Kohli

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.

Responses of Phytochelatins and Metallothioneins in Alleviation of Heavy Metal Stress in Plants: An Overview

Abstract Heavy metal detoxification in plants is a phenomenon resulting from complex interactions among interconnected physiological pathways and defense shunts leading to reactive oxygen species scavenging and subsequent protection of cellular vitals. These signaling pathways involve cross-talk between a number of antioxidant compounds including two main groups of amino acid rich metal chelators, namely the phytochelatins (PCs) and metallothioneins (MTs). This book chapter traces the mechanism of metal tolerance and detoxification strategies possessed by these biological molecules in addition to their biosynthesis, roles played and genetic aspects involved in their course of action. The isolation, characterization of PC and MT genes involved in metal compartmentalization and their successful induction in other plants is a much more recent application because this is of immense importance to the world of agronomics. Genetic validation and success for the same has been reported widely in this decade and many prominent reports have been included in the text to highlight this. Extending this vast information about the PC and MT gene pool at the proteomic level is gaining a lot of momentum currently and shall remain the future line of investigation for understanding metal resistance pathways at the cellular as well as subcellular level.

ROS Signaling in Plants Under Heavy Metal Stress

Contamination of soil with toxic heavy metals is a major reason for retarded growth of crops and harmful effects on human health. Cultivation of large number of agricultural crops in contaminated soil is a major concern of environmentalist in the present times. Increased level of heavy metals can enter in to the food chain and may available for human consumption. Metal toxicity-induced oxidative stress eventually leads to refrained enzyme activities due to displacement of essential cofactors with other metal ions and blocking of functional groups such as carboxyl, histidyl and thiol, and proteins. Oxidative burst releases large quantities of reactive oxygen species (ROS) such as superoxide anion, hydrogen peroxide, hydroxyl radical, singlet oxygen, etc., which is one of the primary response of plants to heavy metal stress. Production of ROS is an inherent feature of plant cell and contributes to the process of oxidative damage leading to cell death. Its production is restricted to several cellular compartments such as mitochondria, chloroplast, and peroxisomes etc. ROS production leads to alteration of several physiological processes including degradation of enzymes, proteins, and amino acids and change in structure of cells. ROS are well described as secondary messengers in variety of cellular processes including acclimatization of cells to stress conditions. The signaling of ROS as a result of oxidative damage is regulated by several other signaling cascades which are interlinked. Their role has been studied under various stress conditions specifically heavy metals which leads to production of NO, H2O2, synthetic electrophilic compounds, lipid peroxidation molecules, etc.

Lignins and Abiotic Stress: An Overview

Lignin is a major carbon sink in the biosphere accounting for about 30 % of total carbon sequestered in terrestrial plants. Being the second most abundant polymer on earth, it is a complex 3-dimensional polymer which is the principal structural component of plant cell wall. The phenylpropanoid pathway is responsible for biosynthesis of a variety of products that include lignin flavonoids and hydroxycinnamic acid conjugates. The phenylpropanoid metabolism has attracted significant research attention as lignin is a limiting factor in a number of agroindustrial processes like chemical pulping, forage digestibility and the processing of lignocellulosic plant biomass to bioethanol. Further, many functions of lignins and related products make the phenylpropanoid pathway essential to the health and survival of plants by providing resistance from abiotic and biotic stresses. These polymers play crucial role in plethora of ecological and biological functions which include shaping of wood characteristics, mechanical support in plants and most importantly stress management (biotic and abiotic stresses). Since lignins act synergistically in a number of agricultural processes, viz. crop production, vigour and disease resistance, thus insights into both the biosynthetic pathway and biodegradation of lignins are of prime significance. Due to the urgent requirement of upregulation and downregulation of lignin genes, focus has been drawn on the genetic engineering of its biosynthetic pathway. This proposed book chapter lays intensive focus on abiotic stress management through lignins by drawing a comparison between the process of lignification of plants under normal conditions as opposed to plants subjected to a variety of abiotic stresses such as drought, flooding, UV rays, heat, chilling and freezing and heavy metal stress.

Jasmonic acid induced changes in physio-biochemical attributes and ascorbate-glutathione pathway in Lycopersicon esculentum under lead stress at different growth stages

Lead (Pb) is one of most toxic heavy metals that adversely affect growth and developmental in plants. It becomes necessary to explore environment safe strategies to ameliorate its toxic effects. Phytohormones play an imperative role in regulating stress protection in plants. Jasmonic acid (JA) is recognized as a potential phytohormone which mediates immune and growth responses to enhance plant survival under stressful environment. The present study was undertaken to evaluate the effect of JA on the growth, metal uptake, gaseous exchange parameters, and on the contents of pigments, osmolytes, and metal chelating compounds in tomato plants under Pb stress during different stages of growth (in 30-, 45-, and 60-day-old plants). We observed a decrease in shoot and root lengths under Pb stress. Treatment of JA improved the shoot and root lengths in the Pb-treated plants. The Pb uptake was increased with the increasing concentrations of Pb, however, seeds pretreated with JA reduced the Pb uptake by the plants. The chlorophyll and carotenoid contents increased by JA treatment in plants under Pb stress. Pre-soaking of seeds in JA, improved gaseous exchange parameters, such as internal CO2 concentration, net photosynthetic rate, stomatal conductance, and transpiration rate under Pb stress. JA enhanced the enzyme activity of ascorbate-glutathione cycle and reduced H2O2 concentration in Pb-treated plants. The contents of osmolyte and metal chelating compounds (total thiols, and non-protein and protein-bound thiols) were increased with the increase in Pb stress. In seeds primed with JA, the contents of osmolytes and metal chelating compounds were further increased in the Pb-treated plants. Our results suggested that treatment of JA ameliorated the toxic effects of Pb stress by reducing the Pb uptake and improving the growth, photosynthetic attributes, activity of ascorbate-glutathione cycle and increasing the contents of osmolytes and metal chelating compounds in the tomato plants.

Microbial Siderophores in Metal Detoxification and Therapeutics: Recent Prospective and Applications

Siderophores are small molecular weight metal scavengers which are released by plants, plant growth-promoting bacterial strains and fungi into the rhizosphere. These molecules have been widely reported as Fe3+ carriers under poor iron ion mobilization; however, recently they are being exposed for affinity towards other metal ions such as copper, zinc, etc. highlighting their phytoremedial potential. They are also effective anti-pathogenic agents, important signals towards oxidative stress and new age therapeutics. To understand the mechanism by which these moieties solubilize metal ions at both genetic and protein levels is the crux of our studies as these are extremely versatile molecules having myriad applications in the fields of agriculture, physiology, drug therapy, diagnosis, etc. Additionally, this paper also covers the biosynthesis and classification of microbial siderophores and their roles in plant and animal physiology.

Antioxidant and Antimutagenic Activities of Different Fractions from the Leaves of Rhododendron arboreum Sm. and Their GC-MS Profiling

In this era of urbanization and environmental pollution, antioxidants and antimutagens derived from plants are promising safeguards for human health. In the current investigation, we analyzed the antioxidant and antimutagenic effects of the hexane, chloroform, and ethyl acetate fractions of Rhododendron arboreum Sm. leaves and determined their chemical composition. The different fractions inhibited lipid peroxidation, repressed the production of nitric oxide radicals, and prevented deoxyribose degradation. The antimutagenic activity of the leaf fractions was analyzed against 4-nitro-O-phenylenediamine, sodium azide and 2-aminofluorene mutagens in two test strains (TA-98 and TA-100) of Salmonella typhimurium. The experiment was conducted using pre- and co-incubation modes. The best results were obtained in the pre-incubation mode, and against indirect acting mutagen. The presence of a number of bioactive constituents was confirmed in the different fractions by GC-MS analysis. The study reveals the strong antioxidant and antimutagenic activity of R. arboreum leaves. We propose that those activities of R. arboreum might correspond to the combined effect of the phytochemicals identified by GC-MS analysis. To the best of our knowledge, this is the first report on the antimutagenic activity of R. arboreum leaves.

Synergistic effect of 24-epibrassinolide and salicylic acid on photosynthetic efficiency and gene expression in Brassica juncea L. under Pb stress

Lead (Pb) has wide-ranging effects on various essential physiological processes in plants including seed germination, root/ shoot growth, photosynthetic efficiency, water status, and activities of enzymes. The effect of combined treatment of 24-epibrassinolide (10-7 M, EBL) and salicylic acid (1 mM, SA) on growth, photosynthetic attributes, and phenolic compounds in 30-, 60-, and 90-day-old plants of Brassica juncea L. under Pb stress (0.25 mM, 0.50 mM, and 0.75 mM) were studied. It was observed that Pb toxicity resulted in lowered growth and photosynthetic efficiency. The expressions of CHLASE, PSY, CHS, and PAL genes were altered. Presoaking treatment with the combination of EBL and SA for metal-stressed plants mitigated the adverse effects of metal stress by improving growth and levels of pigment and phenolic compounds.