Vikramjit Kaur Zhawar

Antioxidant response and Lea genes expression under exogenous ABA and water deficit stress in wheat cultivars contrasting in drought tolerance

Two wheat (Triticum aestivum) cultivars, C306 (drought tolerant) and PBW343 (drought susceptible) were compared for their response to exogenous ABA, water stress (WS) and combined (ABA plus WS) during their seedlings growth. Their responses were studied in the form of seedlings growth, antioxidant potential of roots and shoots and expression levels of LEA genes in shoots. ABA treatment led to increase in levels of ascorbate, ascorbate to dehydroascorbate ratio, antioxidant enzymes and decreases in levels of dehydroascorbate, malondialdehyde (MDA). Decrease in biomass, ascorbate contents, ascorbate to dehydroascorbate ratios and antioxidant enzymes was more in PBW343 than in C306 under WS. Dehydroascorbate and MDA levels were higher in PBW343 than in C306 under WS. ABA plus WS improved some of these features from their levels under WS in PBW343. Proline contents were not increased significantly under ABA in both cultivars. Out of ten LEA genes studied, six LEA genes were induced more under WS than under ABA in C306 but equally induced in PBW343. Four LEA genes were induced earlier in PBW343 but later in C306. Wdhn13 was induced more under ABA than under WS in C306 while it was non-responsive to both stresses in PBW343.

Phytic acid and raffinose series oligosaccharides metabolism in developing chickpea seeds

Phytic acid and raffinose series oligosaccharides (RFOs) have anti-nutritional properties where phytic acid chelates minerals and reduces their bioavailability to humans and other animals, and RFOs cause flatulence. Both phytic acid and RFOs cannot be digested by monogastric animals and are released as pollutant-wastes. Efforts are being made to reduce the contents of these factors without affecting the viability of seeds. This will require a thorough understanding of their metabolism in different crops. Biosynthetic pathways of both metabolites though are interlinked but not well described. This study was made on metabolism of these two contents in developing chickpea (Cicer arietinum L cv GL 769) seeds. In this study, deposition of RFOs was found to occur before deposition of phytic acid. A decline in inorganic phosphorus and increase in phospholipid phosphorus and phytic acid was observed in seeds during development. Acid phosphatase was the major phosphatase in seed as well as podwall and its activity was highest at early stage of development, thereafter it decreased. Partitioning of 14 C label from 14 C-glucose and 14 C-sucrose into RFOs and phytic acid was studied in seeds in presence of inositol, galactose and iositol and galactose, which favored the view that galactinol synthase is not the key enzyme in RFOs synthesis.

Phenolic parameters under exogenous ABA, water stress, salt stress in two wheat cultivars varying in drought tolerance

Phenolic parameters were studied in two wheat cultivars PBW 343 (drought susceptible) and C 306 (drought tolerant) under exogenous ABA, water stress (WS) and salt stress (SS). ABA decreased shoot length and increased root length in both cultivars, where increase of root length was higher in C 306. It increased lignin, phenolics, cell wall-associated peroxidases and polyphenol oxidases (PPOs) in shoots and roots of both cultivars, however, increases in peroxidases and PPOs were higher in C 306, while increases of lignin and phenolics were higher in PBW 343. Under WS and SS, parameters were regulated in almost the same manner as under ABA, except increases of cell wall-associated PPOs were higher in PBW 343 than C 306 under WS. Root lignin content was negatively related to root growth. Cell-wall associated peroxidases were not related to growth or lignin. PBW 343 showed improved growth under SS than WS.

ABA improvement of antioxidant metabolism under water stress in two wheat cultivars contrasting in drought tolerance

Antioxidant metabolism was studied in two wheat cultivars PBW 343 (drought susceptible) and C 306 (drought tolerant) under exogenous ABA, water stress (WS) and ABA plus WS. C 306 showed lesser increases in ROS (superoxide anions) and protein carbonylation in shoots and roots under WS as compared to PBW 343. C 306 did not show increases in glutathione peroxidase, glutathione-S-transferase, total glutathione under WS, while PBW343 showed such increases only at early stage, while at later stages of stress, the decline in levels of these parameters was improved on supplying ABA. Monodehydroascorbate reductase (MDHAR) and dehydroascorbate reductase (DHAR) activity were not induced under ABA in both the cultivars but under WS MDHAR was induced only in C 306, while in case of DHAR greater increase was observed in C 306 than in PBW343.

Antioxidant potential of fresh and after-ripened dry embryos of two wheat cultivars contrasting in drought tolerance

Seed of wheat cv. C 306 was more dormant, higher ABA-sensitive and more desiccated than PBW 343. Dormancy and ABA-sensitivity decreased, and seed moisture content increased during after-ripening, where decrease in ABA-sensitivity was greater in PBW 343. Dry embryo of C 306 contained lesser level of ROS (H2O2 and superoxides) and nitric oxide than that of PBW 343. ROS and nitric oxide increased during after-ripening, and such increase was higher in PBW 343. Dry embryo of C 306 contained higher level of ascorbate, glutathione, lesser level of proline and similar level of phenolics than that of PBW 343. All these non-enzymatic antioxidants except ascorbate decreased during after-ripening. Dry embryo of C 306 showed higher activities of ascorbate peroxidase (APX), catalase (CAT), and lower activity of peroxidase (POX) than that of PBW 343. Activities of APX and CAT did not change, POX decreased, while GR increased during after-ripening, and decrease in POX activity was greater in PBW 343.

ABA-dependent sucrose regulation of antioxidant metabolism in wheat cultivars varying in ABA-sensitivity

Abstract Effect of sucrose and its abscisic acid (ABA) dependence was studied for seed germination, growth and antioxidant related parameters in two wheat cultivars PBW343 (ABA-lesser sensitive) and C306 (ABA-higher sensitive) by using sucrose (Suc) with or without sodium tungstate (inhibitor for ABA biosynthesis) in culture medium. Exogenous Suc (at 1.5% and 3%) inhibited germination in both cultivars where ABA-dependency for such inhibitions was seen only under 3% sucrose in PBW343 and 1.5% sucrose in C306. Exogenous Suc at 1.5% stimulated growth, which was ABA-dependent in both cultivars. Exogenous Suc at 3% inhibited growth in both cultivars but such inhibitions were ABA-dependent only in PBW343. Suc supply (3%) decreased antioxidant enzymes and H2O2 in PBW343 but increased these in C306. These changes were ABA-dependent. Suc supply (3%) increased reduced state of ascorbate in shoots and roots of PBW343 and in shoots of C306, and such increases were ABA-dependent. Suc-induced increases of proline were ABA-independent in both cultivars and were higher in C306.

ABA regulation of post-germination desiccation tolerance in wheat cultivars contrasting in drought tolerance

Post-germination desiccation tolerance (DT) was studied in two wheat cultivars. Effect of pretreatment of abscisic acid (ABA)/ osmotic/ salt/ heat stress was also studied. One day (d)-old seedlings of wheat cultivars PBW 644 (drought tolerant) and PBW 343 (drought susceptible) were exposed to ABA/stress treatment for next 1 d, desiccated for 4 d and subsequently rehydrated for 4 d. Biomass, protein, water, protein carbonyls (oxidative toxicity) and nitric oxide (NO) levels were measured in 2 d (treated), 6 d (desiccated), 10 d (rehydrated) seedlings. Vegetative reactive oxygen species (ROS)/ NO-pathways were studied under normal condition and ABA supply by supplying ROS/NO scavengers. Desiccation caused water loss and increased oxidative toxicity. PBW 644 showed very low level of toxicity but higher loss of water under desiccation. ABA/ stress pretreatment further reduced water level under desiccation and reduced biomass upon rehydration in PBW 644 only. On the other hand, PBW 343 did not show higher decrease of water but showed high toxicity under desiccation where ABA/stress pretreatment improved this response by increasing biomass upon rehydration. This indicated that PBW 644 used metabolic arrest under desiccation for survival while PBW 343 used growth promotive mode. ABA/ROS/NO-pathways were operational in both cultivars.

ABA regulation of antioxidant activity during post-germination desiccation and subsequent rehydration in wheat

ABA regulation of antioxidant activity during post-germination desiccation and subsequent rehydration was studied in two wheat cultivars PBW 644 (ABA-higher sensitive and drought tolerant) and PBW 343 (ABA-lesser sensitive and drought susceptible) where 1 d-germinated seeds were exposed to ABA/ PEG- 6000 for next 1 d, desiccated for 4 d and subsequently rehydrated for 4 d. Ascorbate, dehydrascorbate to ascorbate ratio, malondialdehyde (MDA), hydroxyl radicals, and activities of monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR), alcohol dehydrogenase (AlcDH) and aldehyde dehydrogenase (AldDH) were measured in seedlings just before desiccation (2 d old), desiccated (6 d old) and rehydrated (10 d old) stages. ROS/NO signaling was studied under CT and ABA supply by supplying ROS and NO scavengers. During desiccation, both cultivars showed increase of oxidative stress (dehydroascorbate to ascorbate ratio, MDA, hydroxyl radicals) and antioxidant activity in the form of ascorbate content and AldDH activity while other antioxidant enzymes were not increased. PBW 644 showed higher antioxidant activity thus produced less oxidative stress compared to PBW 343. During rehydration, activities of all antioxidant enzymes and levels of ROS (hydroxyl radicals) were increased in both cultivars and MDA was decreased in PBW 343. ABA supply improved desiccation as well as rehydration by improving all parameters of antioxidant activity tested in this study. PEG supply resembled to ABA-supply for its effects. ABA/PEG improvements were seen higher in PBW 644. ROS/NO-signalling was involved under CT as well as under ABA for increasing antioxidant activity during desiccation as well as rehydration in both cultivars.

Hydrogen peroxide and nitric oxide regulation of phenolic metabolism under water stress and ABA in wheat

Wheat cultivar PBW644 (drought tolerant) and PBW343 (drought sensitive) were found as ABA-higher sensitive and ABA-lesser sensitive, respectively, in the screen of six wheat cultivars. Both cultivars were studied for H2O2 (ROS)/nitric oxide (NO)-regulation of growth and phenolic metabolism under ABA and water stress (WS) by supplying ROS/NO producers as well as scavengers. Endogenous ROS/NO under ABA/WS increased growth, such effect was higher in PBW644. In PBW343, reduced growth under WS was improved by exogenous ROS/NO. Exogenous ROS/NO under ABA/WS decreased lignin and increased phenolics in PBW343 but such relation was not found in PBW644. Endogenous NO under WS increased flavonoids in both cultivars. Both ROS/NO under ABA/WS increased flavonoids in PBW644, however, in PBW343, only ROS increased these in roots. Under WS, PBW644 showed higher levels of cell wall peroxidase (CW-POX) and lower levels of soluble peroxidase (S-POX) than PBW343. However, under ABA, it showed higher levels of both peroxidases. ROS/NO signals under ABA increased both types of POX in both cultivars while under WS, these signals increased both types in PBW343 but CW-POX only in PBW644. Polyphenol oxidases were ABA-upregulated in PBW644 only. Under WS, these enzymes were maintained higher in PBW343. This study indicated that tolerant cultivar under WS contained sufficient endogenous ROS/NO signalling to which susceptible cultivar lacked but showed improvement on exogenous applications. Secondly, tolerant cultivar was using less phenolic activity under WS which could be due to the presence of sufficient levels of primary antioxidants.

Antioxidant parameters under salt stress in drought tolerant and susceptible wheat cultivars

Antioxidant parameters were studied under salt stress in shoots and roots of two wheat cultivars PBW 343 (drought sensitive) and C 306 (drought tolerant). Compared to C 306, PBW 343 showed higher activities of monodehydro-ascorbate reductase, glutathione-S-transferase, glutathione peroxidase in shoots and roots and higher levels of redox state of glutathione in roots under salt stress, but it also showed large increases in oxidative toxicity in terms of protein carbonyls and lower levels of nitric oxides in shoots and roots. Almost no increase in protein carbonyls accompanied with absence of increases in antioxidants under salt stress in C 306 indicated the presence of different antioxidants under salt stress in C 306.