Repeated water deficit events trigger adjustments in enzymatic antioxidant system in oil palm

Plants are able to reprogram their metabolism to cope with drought stress based on previous signals of water deficit events. Recently, we reported that oil palm seedlings exposed to three water deficit cycles attenuate oxidative damage on the photosynthetic machinery when compared to those facing drought conditions for the first time. However, the mechanism underlying the photosynthetic apparatus maintenance at either single or repeated events of drought stress is not well understood. Herein, oil palm seedlings were investigated for their photosynthesis acclimation upon single (1WD) and repeated (3WD) events of drought by assessing leaf gas exchange, chlorophyll fluorescence, and biochemical variables when predawn leaf water potential of stressed plants reached about –1.7 MPa (Day 7) and 2.5 MPa (Day 28). Plants of 1WD treatment exhibited higher chlorophyll degradation, higher membrane lipid peroxidation, and lower photosystem II activity than both control and 3WD plants. In contrast, 3WD plants exhibited low hydrogen peroxide coupled with upregulation of the enzymatic antioxidant system. The outcomes suggest that the acclimation of oil palm plants to repetitive water deficit events is related to the adjustments in antioxidant enzyme activities to attenuate oxidative damage to the photosynthetic machinery.