Authors:Rattanpreet Kaur and Vikramjit Kaur Zhawar
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.
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.