Effect of drought stress on physiological changes and leaf surface morphology in the blackberry

The blackberry (Rubus L.) is a berry fruit with high capacity for drought stress tolerance. In this study, the rooted clones of blackberry cv. ‘Kiowa’ growing in pots and produced by tissue culture were subjected to 14 days of drought stress for investigation of the physiological changes and leaf morphological characteristics. After the treatment, the leaf relative water content (RWC) on days 10 and 14 was significantly lower than that of the controls. Accordingly, the stress imposed an evident increase in the leaf electrolyte leakage. The superoxide dismutase activity under drought stress gradually decreased; meanwhile, the peroxidase activity displayed a higher level. At the elongation stage, both ascorbic acid (AsA) and glutathione (GSH) accumulation revealed a rising trend. Afterward, micromorphological observation revealed that with the increasing duration of stress, cellular morphology of the leaf epidermis endured a series of expansion changes. Moreover, the drought progression seemingly enhanced the stomatal length on day 7, and the stomatal width and opening on day 10, respectively. By day 14, the treated leaves demonstrated a striking increase in stomata density than before. Cell walls of the leaf epidermal and spongy tissue cells were thickened with prolonged drought. In particular, from day 10, the spongy tissue cells were clearly squeezed and filled with sclerenchyma. These results indicated that blackberry clones exhibited adaption to drought, which was reflected by the changes in leaf RWC, electrolyte leakage and antioxidative enzyme activities, the elevation of AsA and GSH concentrations and responses of leaf micromorphology.