Geetika Sirhindi

Jasmonic Acid Modulates the Physio-Biochemical Attributes, Antioxidant Enzyme Activity, and Gene Expression in Glycine max under Nickel Toxicity

In present study, we evaluated the effects of Jasmonic acid (JA) on physio-biochemical attributes, antioxidant enzyme activity, and gene expression in soybean (Glycine max L.) plants subjected to nickel (Ni) stress. Ni stress decreases the shoot and root length and chlorophyll content by 37.23, 38.31, and 39.21%, respectively, over the control. However, application of JA was found to improve the chlorophyll content and length of shoot and root of Ni-fed seedlings. Plants supplemented with JA restores the chlorophyll fluorescence, which was disturbed by Ni stress. The present study demonstrated increase in proline, glycinebetaine, total protein, and total soluble sugar (TSS) by 33.09, 51.26, 22.58, and 49.15%, respectively, under Ni toxicity over the control. Addition of JA to Ni stressed plants further enhanced the above parameters. Ni stress increases hydrogen peroxide (H2O2) by 68.49%, lipid peroxidation (MDA) by 50.57% and NADPH oxidase by 50.92% over the control. Supplementation of JA minimizes the accumulation of H2O2, MDA, and NADPH oxidase, which helps in stabilization of biomolecules. The activities of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and ascorbate peroxidase (APX) increases by 40.04, 28.22, 48.53, and 56.79%, respectively, over the control in Ni treated seedlings and further enhancement in the antioxidant activity was observed by the application of JA. Ni treated soybean seedlings showed increase in expression of Fe-SOD by 77.62, CAT by 15.25, POD by 58.33, and APX by 80.58% over the control. Nevertheless, application of JA further enhanced the expression of the above genes in the present study. Our results signified that Ni stress caused negative impacts on soybean seedlings, but, co-application of JA facilitate the seedlings to combat the detrimental effects of Ni through enhanced osmolytes, activity of antioxidant enzymes and gene expression.

Effects of 24-epibrassinolide and 28-homobrassinolide on the growth and antioxidant enzyme activities in the seedlings of Brassica juncea L.

The present paper deals with the effects of two active forms of brassinosteroids (BRs) as epibrassinosteroid (24-EBL) and homobrassinosteroid (28-HBL) on percentage germination, growth in the form of shoot length, activities of auxinase (IAAO), polyphenol oxidase (PPO), superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APOX) in 10 day old seedlings of Brassica juncea L. (RCM 619) under field conditions. Exogenous application of 240-EBL and 28-HBL significantly ameliorate the total protein content as compared to untreated control seedlings. 10−8 M 28-HBL helps in enhancing the PPO activity very significantly, as compared to all other concentrations of EBL and HBL and also to that of untreated control. Similar trend was observed in IAAO activity. It was observed that all the concentrations of EBL were unable to enhance the APOX activity as compared to untreated control seedlings but 10−8 M HBL significantly ameliorates APOX activity. CAT and SOD activities ameliorate significantly with exogenous application of EBL and HBL. Out of two active forms of BRs, 28-HBL was more effective at germination stage in scavenging the free radicals, which are produced in greater amount during germination from basic metabolic processes, whereas 28-EBL was effective in the initial growth of seedlings in the form of increase in shoot length.

Brassinosteroids: Biosynthesis and Role in Growth, Development, and Thermotolerance Responses

Brassinosteroids are new and unique class of plant growth regulators that constitutes the sixth class of phytohormones. Till date more than 70 analogues of these natural occurring and nonnatural analogues of brassinolides (BL) have been identified from different plant species. Brassinoslides due to their ubiquitous presence in plant species in almost all parts of plant orchestrate myriad growth and developmental processes. Owing to their peculiar structural features, their extremely low abundance in natural sources, and potent biological activity, BLs are being studied intensively to understand their role in plant metabolism under normal and inadequate growth conditions. Their main physiological effects in plants include cell division control, germination and growth promotion, regulation of hormonal balance, activation of protein and nucleic acid synthesis, enzyme activity, and most interestingly increased resistance to abiotic and biotic stresses. Exogenous application of BLs to plants at seed level or as foliar spray enhances antioxidant defense activities, and accumulation of osmoprotectants such as proline and glycine betaine under stress conditions illustrated antistress properties of brassinosteroids. BLs reported to play a regulatory role in the control of cell-cycle progression and differentiation in the Arabidopsis, and other plants may offer a novel therapeutic strategy for various diseases.

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.

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.

Genome-wide characterization and expression profiling of TIFY gene family in pigeonpea (Cajanus cajan (L.) Millsp.) under copper stress

Copper is a vital micronutrient for plant growth and development, but in high concentration it leads to the oxidative damage thereby initiating biosynthesis of jasmonic acid (JA). The JA signalling is mediated by various transcription factors (TFs) such as JAZ and MYC2. JAZ TFs are the negative regulators of JA signalling which are degraded in presence of JA. JAZ proteins belong to TIFY family and regulate various biological processes such as plant development, response to phytohormones, biotic and abiotic stresses. In the present study, we identified 18 TIFY family proteins in pigeonpea, which are further classified into TIFY, JAZ and ZML subfamilies. Gene expression of 12 CcTIFY genes in pigeonpea was studied under methyl jasmonate (Me-JA), JA in presence and absence of copper (Cu). Our results showed that the transcript levels of CcTIFY3, CcTIFY4, CcTIFY5, CcTIFY9 and CcTIFY16 were upregulated under Cu stress, indicating their involvement in Cu stress signalling. The presence of defense and stress responsive cis-regulatory elements in the promoter regions of these genes further confirms their involvement in response to Cu stress. Apart from feedback regulation of JAZ proteins, the expression of CcTIFY3 and CcTIFY9 was observed to be upregulated in Me-JA and JA treatment, respectively, which suggest involvement of alternative JA and Me-JA signalling.

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.

28-Homobrassinolide-Induced Exaggerated Growth, Biochemical MolecularAspects of Brassica Juncea L. RLM-619 Seedlings under High TemperatureStress

The present study was pertaining to study the mechanism and signaling of BRs under high temperature stress in Brassica juncea L. plants. Results advised that high temperature stress reduced the shoot length, root length, fresh weight of the plants but 28-homobrassinosteroids (28-homoBL) treatment reduced the toxic effect of high temperature stress by improving the same of B. juncea L. plants. To ascertain these free radical scavenging enzymes (superoxide dismutase (SOD), Catalase (CAT), Peroxidase (POD), Ascorbate peroxidase (APOX), Polyphenol oxidase (PPO) and Indole acetic acid oxidase (IAAO) and lipid oxidation (MDA) were assayed along with photosynthetic pigments, total carbohydrates, reducing sugars and non-reducing sugars. All studied scavenging enzymes activities were ameliorated by the homoBL treatments. The pigments decreased under temperature stress were also protected by homoBL treatments. Proteins profiling by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDSPAGE) were also studied to know the behavior of proteins under temperature stress as well as with the treatment of homoBL. Protein bands disappeared in temperature stress while in the presence of homoBL treatment existing proteins displayed more accumulation leading to the appearance of new bands. Native-PAGE of SOD, CAT and POD suggested the presence of in isoenzymic forms in cells. Application of different concentration of homoBL increased intensities of these isoenzymes under temperature and normal condition as compared to control untreated seedlings. The gene expression of SOD and CAT also suggested that synthesis these enzymes were decreased under high temperature stress but ameliorated with the treatment of homoBL. Present study demonstrated that 28-homoBL have stress-ameliorative properties in B. juncea seedlings exposed to high temperature stress by improving seedling growth and enhancing protein content as well as activities of SOD, CAT, APOX, PPO and IAA Oxidase. Further, it was suggested by decreasing the MDA content after the treatments of 28-homoBL. This study demonstrate the culmination of BR’s as an anti-stressor for protection of plant exposed to high temperature stress but extensive studies are still needed to know the various aspects related to stress and role of brassinosteroids in regulating them at molecular and signaling level.

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.

28-homobrassinolide regulates antioxidant enzyme activities and gene expression in response to salt- and temperature-induced oxidative stress in Brassica juncea

Brassinosteroids (BRs) are a group of naturally occurring plant steroid hormones that can induce plant tolerance to various plant stresses by regulating ROS production in cells, but the underlying mechanisms of this scavenging activity by BRs are not well understood. This study investigated the effects of 28-homobrassinolide (28-HBL) seed priming on Brassica juncea seedlings subjected to the combined stress of extreme temperatures (low, 4 °C or high, 44 °C) and salinity (180 mM), either alone or supplemented with 28-HBL treatments (0, 10−6, 10−9, 10−12 M). The combined temperature and salt stress treatments significantly reduced shoot and root lengths, but these improved when supplemented with 28-HBL although the response was dose-dependent. The combined stress alone significantly increased H2O2 content, but was inhibited when supplemented with 28-HBL. The activities of superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APOX), glutathione reductase (GR), dehydroascorbate reductase (DHAR) and monodehydroascorbate reductase (MDHAR) increased in response to 28-HBL. Overall, the 28-HBL seed priming treatment improved the plant’s potential to combat the toxic effects imposed by the combined temperature and salt stress by tightly regulating the accumulation of ROS, which was reflected in the improved redox state of antioxidants.