Five varieties of wheat (Triticum aestivum L.) -KW, UP 2752, PBW 343, SO and LV -were subjected to water stress and sampling was done on the 3 rd , 6 th and 9 th day of stress. RWC decline in KW, UP 2752 and PBW 343 (36.65, 42.34 and 40.75% respectively) was comparatively lesser than in LV and SO (52.93 and 52.67% respectively). In all varieties tested, three antioxidant enzymes (POX, APOX and GR) showed an initial increase. The activity of POX and GR increased with the increase in the duration of stress in KW, UP 2752 and PBW 343, while the activity of APOX declined. However, CAT and SOD showed an initial increase in these varieties, whereas it declined in SO and LV with increase in the period of stress. Accumulation of H 2 O 2 declined during prolonged water stress in KW, UP 2752 and PBW 343, while it increased in LV and SO. The accumulation of MDA content was three times higher in susceptible varieties than in tolerant varieties. The content of proline, phenol and ascorbate increased during water stress whereas the accumulation of carotenoid showed a significant decrease after showing an initial increase in the tested varieties. Higher values of total antioxidant and MSI were recorded in KW, UP 2752 and PBW 343 during stress while after 6 days MSI declined in LV and SO. During water stress there was a general decline in the total chlorophyll content. Analyzing the data, the present work suggested that out of the five varieties, KW, UP 2752 and PBW 343 showed more tolerance to water stress than SO and LV.Keywords: antioxidants, carotenoids, drought, lipid peroxidation.Abbreviations: APOX: ascorbate peroxidase (EC.1.11.1.11); CAT: catalase (EC.1.11.1.6); CMS: cell membrane stability; DAB: diaminobenzidine; EC: electrical conductivity; GR: glutathione reductase (EC 1.6.4.2); H 2 O 2 : hydrogen peroxide; KW: Kaweri; LV: local variety; MDA: malondialdehyde; MSI: membrane stability index; NBT: nitro blue tetrazolium; PPO: polyphenol oxidase; POX: peroxidase (EC. 1.11.17); RH: relative humidity; ROS: reactive oxygen species; RWC: relative water content; SO: Sonalika; SOD: superoxide dismutase (EC 1.15.1.1); TBA: thiobarbituric acid; TCA: trichloroacetic acid.Oxidative stress in five wheat varieties (Triticum aestivum L.) exposed to water stress and study of their antioxidant enzyme defense system, water stress responsive metabolites and H 2 O 2 accumulation
Abiotic stress responses are of the utmost importance for plants because they cannot survive unless they are able to cope with environmental changes, such as high and low temperatures, drought, flooding, salinity, freezing, change in pH, strong light, UV, and heavy metals. Plants respond to various stresses at different levels, including molecular and cellular levels, as well as by modifying their metabolomes. Hence, studies on plant responses to stresses can be conducted at any of these levels to provide an understanding of the mechanisms involved. The present chapter focuses on the metabolomic approach to understand the responses of plants to different abiotic stresses, which can then be utilized to evolve strategies to combat such stress. Osmoprotectant metabolites, such as proline, glycine betaine, and polyamines, as well as carbohydrates, play important roles in the protection of plants against osmotic disbalances due to abiotic stresses. In addition, oxidative stresses are also overcome by an array of antioxidants, such as phenols, ascorbate, carotenoids, and a-tocopherol, as well as antioxidative enzymes. Signaling cascades activated during abiotic stresses lead to overexpression of protein kinases and stress proteins, and also involve molecules such as jasmonic acid and salicylic acid. Protein kinases and protein phosphatases that are encoded by large gene families often act in tandem to perform the phosphorylation and dephosphorylation leading to their activation and inactivation involved in stress signaling in plants. Analysis of microRNAs and transcriptomes has provided sufficient understanding of the gene expression levels during periods of stress. Hence, taken together, all these results can be utilized for identifying genes and/or metabolites overexpressed in tolerant species during periods of stress, and can be utilized to achieve higher tolerance and survivability during stresses. 727
One month old plant of four varieties (MW, KD, GY and GN) of wheat (Triticum aestivum L.) was taken and subjected to water stress for 3, 6 and 9 days. RWC was found to be higher in case of GY and KD when compared to MW and GY. There was an initial enhancement in the activities of all five tested antioxidative enzymes- peroxidase, ascorbate peroxidase, catalase, glutathione reductase and superoxide dismutase in K and GN varieties, while in MW and GY, the activity of catalase and superoxide dismutase showed a decline at all periods of water stress. Peroxidase and glutathione reductase activities increased even on 9th day of stress in K and GN, but all other activities showed a decline after 3 days of stress. The accumulation of H202, showed an increase with increasing days of water stress but in K and GN there was a decline during prolonged water stress. Lipid peroxidation increased significantly which was higher in case of MW and GY. With increase in the duration of water stress proline, phenol and ascorbate content increased. Higher values of MSI and total antioxidant were observed in the cultivar KD and GY with increase in the severity of water stress than in MW and GY. After an initial enhancement the content of carotenoid increased followed by a decline. Total chlorophylls showed a general decline during water stress, but the ratio of chla/b showed an initial increase in the 3rd day of water stress which declined during the latter stages of water stress. Results of the present study indicate that two of the varieties- MW and GY are susceptible to water stress, while the other two-K and GN is tolerant.
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