Physiological responses of blackberry cultivar 'Ningzhi 1' to drought stress

In order to study the potential antioxidant defense mechanisms, the blackberry cultivar 'Ningzhi 1', a new floricane-fruiting hybridberry (Rubus sp.), was subjected to 20-day drought stress by withholding irrigation, followed by rewatering for 5 days, then the leaf water content (LWC), membrane electrolyte leakage, contents of photosynthetic pigments, protein, soluble sugar, hydrogen peroxide (H2O2), and MDA, activities of superoxide dismutase (SOD) and peroxidase (POD), and the levels of antioxidants such as ascorbate (AsA) and reduced glutathione (GSH) in leaves were investigated. The results showed that LWC was greatly decreased during the 20-day drought treatment period. After rewatering, water content restored. Drought stress induced significant accumulation of photosynthetic pigments, protein, soluble sugar, H2O2, and MDA as well as an increase in membrane electrolyte leakage, which were all decreased after rewatering. The activities of SOD and POD were elevated under drought stress, which were still at higher levels compared with control after rewatering. The contents of AsA and GSH ascended first and were then followed by a decline during the whole drought period, after rewatering, the contents increased and remained at a higher level than that of controls. The plants showed a rapid and almost complete recovery after rewatering, and the physiological alterations could represent a set of adaptive mechanisms employed by 'Ningzhi 1' to cope with drought stress. It was suggested that increased drought tolerance of 'Ningzhi 1' was due to higher antioxidant enzymes, reduced lipid peroxidation, better accumulation of osmolytes, and maintenance of tissue water content.