The C3-CAM shift is crucial to the maintenance of the photosynthetic apparatus integrity in Pereskia aculeata under prolonged and severe drought

Abstract

This work aimed to evaluate how the C3-CAM shift could contribute to photoprotection and attenuate losses of CO₂ uptake in Pereskia aculeata plants under water stress. Plants were subjected to treatments: well-watered (WW), water deficit (WD), and recovery (Rec) in two experimental conditions (greenhouse and growth chamber). Induction of the C3-CAM shift by drought was assessed by leaf acidification, carbohydrate content, photochemical activity, gas exchange, and stomata density and closure during diurnal and nocturnal periods. Leaf acidity was reduced during the night period in WW-plants and increased in WD-plants, suggesting active accumulation of organic acids associated with CAM induction by drought. This apparent CAM induction in WD-plants was associated to increase carbohydrates and significant reduction of leaf water potential (Ψ_W). WD-plants showed a positive carbon balance associated with a higher net-CO₂ uptake (P_N) during night period compared to WW-plants. Moreover, WW-plants presented negative values for P_N associated with a negative carbon balance at night. In both conditions (WW and WD) plants showed P_N near zero at night. However, a positive carbon balance associated with a slight stomatal aperture at during the day and strong closure during night in the WD-plants, suggests that C3-CAM shift, able to maintain CO₂ uptake, presented a better trend toward the CAM-cycling model. Together, this study shows that CO₂ uptake conferred by C3-CAM shift under drought contributed to photoprotection and better photosynthetic recovery after rehydration of Pereskia aculeata plants.