REGULATION OF PEA CYTOSOLIC ASCORBATE PEROXIDASE AND OTHER ANTIOXIDANT ENZYMES DURING THE PROGRESSION OF DROUGHT STRESS AND FOLLOWING RECOVERY FROM DROUGHT

The molecular mechanism underlying the regulation of the expression of Apxl, the gene encoding cytosolic ascorbate peroxidase, as well as other antioxidant enzymes, was studied during the progression of drought stress and following recovery from drought. Increase in steady-state transcript levels of the cytosolic isozymes of ascorbate peroxidase and Cu/Zn-superoxide dismutase paralleled the increase in stomatal resistance during drought stress, but was even more dramatically enhanced following recovery from drought. Cytosolic Cu/Zn-superoxide dismutase and ascorbate peroxidase and chloroplastic Cu/Zn-superoxide dismutase protein and activity increased during drought stress and following recovery. In contrast, catalase activity increased during drought stress but returned to normal levels following recovery. During recovery from drought stress, cytosolic ascorbate peroxidase expression was regulated post-transcriptionally at the level of protein synthesis. The transcription rate of the Apxl gene, as determined by nuclear run-on assay, increased during drought stress and at 10 h following rewatering.