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 ot her 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 an d Cu/Zn-superoxide dismutase paralleled the increase in stomatal resis tance during drought stress, but was even more dramatically enhanced f ollowing recovery from drought. Cytosolic Cu/Zn-superoxide dismutase a nd ascorbate peroxidase and chloroplastic Cu/Zn-superoxide dismutase p rotein and activity increased during drought stress and following reco very. In contrast, catalase activity increased during drought stress b ut returned to normal levels following recovery. During recovery from drought stress, cytosolic ascorbate peroxidase expression was regulate d post-transcriptionally at the level of protein synthesis. The transc ription rate of the Apxl gene, as determined by nuclear run-on assay, increased during drought stress and at 10 h following rewatering.