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.