Physiological and Biochemical Responses of Citrus Seedling Rootstocks to Drought Stress and After Rewatering

Responding mechanisms to water stress were evaluated for 8-month-old seedling rootstocks of Mexican lime, sour orange, volkameriana and rangpur lime in greenhouse conditions. Watering regime was withholding water for 14 days and then rewatering for 3 days at field capacity. Physiological and biochemical indices were evaluated in seedlings leaves at a minimum of two times (end of drought stress and rewatering periods). According to the results, drought led to a significant reduction in the water potential and relative water content of all rootstocks compared to controls, but all differences disappeared after rewatering. Evaluation of the maximum quantum yield of photosystem 2, malondialdehyde content and ion leakage showed that the photosynthetic apparatus of rootstocks, except for volkameriana, was oxidatively damaged due to photoinhibition, but only sour orange had no ability to recover its normal physiological condition after rewatering. According to data analysis, the decreased chlorophyll content of Mexican lime and rangpur lime leaves under stress was likely to be part of the mechanisms responsible for alleviating photoinhibition-related oxidative damage to the photosynthetic apparatus. Under stresss, the chlorophyll content of volkameriana and sour orange leaves was increased and decreased, respectively; which was irreversible for sour orange. Enzymatic antioxidant efficiency of volkameriana, Mexican lime and rangpur lime seedlings under water stress was appropriate and improved by rewatering resulting in acclimation to stress conditions. In conclusion, volkameriana rootstock had the best performance in stress tolerance compared to other evaluated rootstocks. Mexican lime and Rangpur lime had similar physiological and biochemical reactions to water stress and rewatering. The sour orange rootstock had no ability to show appropriate reactions to stress or to recover its normal condition after rewatering.