Biochemical Changes in <i>Vitis vinifera</i> Buds between Dormancy and Forced Bursting: A Case Study of Three Portuguese White Varieties

The transition between the dormancy and budburst is accompanied by physiological and biochemical changes, which include variations in the carbohydrates, enzymatic activity, as well as hormones present inside the buds. The present study aimed to evaluate the biochemical changes that occur in dormant buds and forced bursting of three <i>Vitis vinifera</i> L. white varieties (Alvarinho, Fernão-Pires, and Loureiro) from two vineyards located in the Vinhos Verdes Demarcated Region, NW Portugal. For this purpose, the contents of malondialdehyde (MDA), proline, carbohydrates, and gibberellic acid (GA₃), as well as antioxidant enzymes activity were analysed. The results showed that the MDA, proline, total soluble sugars, and GA₃ contents tended to be higher at budburst. In contrast, the starch content was higher at dormancy. The enzymatic activities of ascorbate peroxidase (APX), peroxidase (POX), and superoxide dismutase (SOD) were lower at budburst, compared with dormancy, while the reverse was observed in catalase (CAT). Significant differences were also observed between varieties for most biochemical parameters analysed, with the exception of CAT activity. Alvarinho stood out from other varieties for presenting higher MDA, proline, soluble sugars, and GA₃ content, while Fernão-Pires displayed higher values of APX and POX activities and starch content. To our knowledge, the present work is the first attempt to examine the biochemical changes in dormant buds and bursting, which determine the vegetative and reproductive continuity of grapevines. This information contributes to better vineyard management, particularly important in light of the climate change scenarios, which can affect the biochemical mechanisms of the buds and compromise the yield and quality of grapevines.