Effects of different irradiance levels on some antioxidant enzymes and on malondialdehyde content during rewatering in olive tree

The effects of water recovery on the activities of superoxide dismutase (SOD; EC 1.15.1.1), catalase (CAT; EC 1.11.1.6), ascorbate peroxidase (APX; EC 1.11.1.11), guaiacol peroxidase (POD; EC 1.11.1.7), polyphenol oxidase (PPO; EC 1.30.3.1) and lipoxygenase (LOX; EC 1.13.11.12), and on malondialdehyde (MDA) levels were investigated in 2-year-old Olea europaea L. (cv. “Coratina”) plants grown in environmental conditions characterized by high temperatures and irradiance levels and gradually subjected to a controlled water deficit. After reaching the maximum level of water stress, plants were subjected to a rewatering treatment for 30 days, under both environmental irradiance and semi-shade conditions. The activities of SOD, CAT, APX, POD and LOX, and MDA levels decreased during the rewatering period in both leaves and roots and these decrements were faster in plants rewatered in semi-shade conditions (SHP) than in plants under environmental light (NSHP). In contrast, PPO activity increased during rewatering in both leaf and root tissues. Thus, the lower expression of the enzymatic antioxidant system in SHP with respect to NSHP may be due to a reduced need of activated oxygen species removal. On the contrary, in NSHP, higher enzyme activities are required for a better protection against a more pronounced oxidative stress.