Allometric and biochemical responses of grapevines subjected to drought and enhanced ultraviolet‐B radiation

Background and Aims: The aim of this study was to evaluate differences in adaptive responses in grapevines (Vitis vinifera L. cv Soultanina) exposed to either drought, enhanced ultraviolet‐B (UV‐B) radiation or the combination of the two environmental stresses. Methods and Results: Results indicated pronounced effects on allometric parameters in plants exposed to the enhanced UV‐B radiation. The combined application of drought and enhanced UV‐B radiation considerably affected shoot growth rate and leaf dry weight. Guaiacol peroxidase (GPX, EC 1.11.1.7), ascorbate peroxidase (APX, EC 1.11.1.11), superoxide dismutase (SOD, 1.15.1.1) and catalase (CAT, 1.11.1.6) activities increased significantly in the enhanced UV‐B radiation treatment. Drought resulted in a significant increase in proline concentration, while the exposure of plants to enhanced UV‐B radiation resulted in the production of UV‐B absorbing compounds (UV_abs). Conclusions: Under drought conditions proline accumulation seemed to be the main mechanism of adaptation contributing to plant's antioxidant defence. On the other hand, under enhanced UV‐B radiation, the accumulation of the UV‐B absorbing compounds and the increase in antioxidant enzymes activities constitute the main mechanisms of grapevine adaptation. Significance of the Study: The data obtained indicate the occurrence of two different mechanisms of adaptation in response to the stressor applied. Furthermore, the patterns of proline and UV_abs concentration changes under stress conditions suggest that the biosynthesis of these two compounds might follow competing metabolic pathways.