INDUCTION OF ENZYMES INVOLVED IN THE ASCORBATE-DEPENDENT ANTIOXIDATIVE SYSTEM, NAMELY, ASCORBATE PEROXIDASE, MONODEHYDROASCORBATE REDUCTASEAND DEHYDROASCORBATE REDUCTASE, AFTER EXPOSURE TO AIR OF RICE (ORYZA-SATIVA) SEEDLINGS GERMINATED UNDER WATER

The activities of enzymes involved in the antioxidative system are low er in rice (Oryza sativa) seedlings that have been germinated under wa ter than in aerobically grown controls and these activities increase w hen the submerged seedlings are transferred to air, In this study, we examined the changes in protein levels of enzymes implicated in the as corbate-dependent antioxidative system, namely, ascorbate peroxidase ( APX), monodehydroascorbate reductase (MDAR), and dehydroascorbate redu ctase (DHAR). We found two isozymes of APX and of MDAR, and one form o f DHAR in rice, The isozymes of MDAR and DHAR were distributed ubiquit ously in rice tissues, but no APX isozyme was found in dry seeds, The levels of all antioxidative proteins were low in submerged seedlings, but repression of their expression was released by transfer of the see dlings to air, However, the levels of some isozymes rose slowly and gr adually, while levels of others rose quickly and then fell again.