Plants retain the preceding abiotic stress memory that may aid in attainment of tolerance to subsequent stresses. In response to drought, plants evolve stress tolerance mechanisms at morphological, physiological and molecular level. For example osmotic adjustment, through accumulation of osmolytes, helps plants survive and have better growth, under drought. So, although drought stress suppressed the growth and yield of crops, however, the plants formerly exposed to one type of stress may develop tolerance/protection to another kind of stress through enhanced production of secondary metabolites. In this study, the factors involved in drought acclimation process and their role in inducing freezing tolerance were investigated in two grape ( Vitis vinifera L.) cultivars. The experiment was set up as split plot in completely randomized design with two factors, including grape cultivars at two levels (Asgari (resistant to drought ) and Yaghouti (sensitive to drought)) and drought stress (control or well-watered, drought stress by withholding irrigation for 12 days, and re-irrigation (recovery) of drought stressed plants). Following drought stress, leaf, stem and root tissues were harvested for analysis of freezing tolerance (lethal temperature resulting in 50% mortality, LT 50 ). The results showed that withholding irrigation increased malon dialdehyde (MDA), proline, glutathione (GSH) contents as well as ascorbate peroxidase (APX) and catalase (CAT) activity. On the other hand drought treatment reduced the relative water content (RWC), chlorophyll fluorescence (Fv/Fm), total chlorophyll, carotenoid, ascorbic acid (AsA), potassium, and protein and starch concentrations. After 7 days of rewatering, RWC, chlorophyll content, Fv/Fm and carotenoids increased to the near of well-watered control level. The cultivar Askari through better control of lipid peroxidation and leaf water content, increased Fv/Fm, increased chlorophyll, carotenoid, proline, and soluble carbohydrates appear to be more drought-resistant than Yaghuti cultivar. Also, the lowest LT 50 was detected in this cultivar. Overall, the highest cold hardiness (lowest LT 50 ) was recorded in stem tissue, in drought resistant cultivar and following drought stress treatment. In all three sampled tissues, when drought-pretreated tissues were exposed to freezing stress, the lower rate of LT 50 under minimum temperature conditions was obtained in comparison to freezing treatment alone. Keywords : Abiotic stress, Stress memory, Ion leakage, Freezing
