Effect of cold stress on water relations, photosynthetic pigments and antioxidant enzymes in olive seedlings

European olive (Olea europaea L.), an evergreen woody plant, is relatively tolerant to cold and drought and its cultivation in semi-arid regions is an important strategy. In this work, the response of olive cultivar 'Zard' to chilling and freezing are evaluated in a completely randomized design. Two-year-old olive seedlings were exposed at temperature of -10, -5, 2 and 10 degrees C for 3 and 6 hours. Relative water content (RWC), water potential (WP), electrolyte leakage (EL), photosynthetic pigments content [including chlorophyll (Chl) a, Chl b, Chl a/b, total chlorophyll (Chl(TOT)) and carotenoid], Chl(TOT)/ carotenoid ratio were determined at the end of the treatments. Likewise, the specific activities of some antioxidant enzymes, such as superoxide dismutase (SOD), catalase (CAT) and peroxidase (POX), were also measured in leaf extracts at the same time. The effect of temperature and duration of cold treatment and their interaction were significant on EL and SOD activity. Both pigment content and antioxidant enzyme activities were influenced by temperature but Chl(TOT) and enzymes of SOD and POX differed significantly in relation to the duration of the cold treatment. RWC and WP were changed by temperature and also by duration of cold treatment. With increasing the cold stress (from 10 to -10 degrees C), RWC, WP and photosynthetic pigments decreased but SOD, PDX and CAT activities increased. However, the increase in the activities of antioxidant enzymes was not enough to eliminate the damage induced by oxidative stress. This study evidenced as events of low temperature (below 10 degrees C) during the cultivation of olive (cultivar 'Zard') induced alteration in plant physiology. From a practical standpoint, the results could be used as approximate tools to determine whether the temperature conditions in a proposed new growing region are appropriate for achieving sustainable oil productivity and quality.