Flavonol-Antioxidant Enzyme Interactions Mediate Grape Skin Acclimation to UV Radiation During Berry Development

Elevated ultraviolet (UV) radiation resulting from climate change influences secondary metabolism in grapevines. In this study, we investigated grape berry responses to varying UV exposures under field conditions (2020-2021), using optical filters to selectively modify the UV spectrum. Our aim was to assess flavonoid accumulation, antioxidant enzyme activities, and the expression of related genes of grape skins in response to different UV exposures. Extending the UV spectrum to include UV-B increased flavonol and anthocyanin concentrations. It also altered the composition of flavonoids, particularly after veraison. Mantel's test revealed a close correlation between flavonol profiles and antioxidant enzyme activities, suggesting a coordinated mechanism in grapevine UV acclimation. Structural equation modelling further showed that trihydroxy flavonols were negatively associated with ascorbate peroxidase (APX) activity, while both di- and trihydroxy flavonols were positively associated with peroxidase (POD) activity under UV exposure. These findings suggest that specific flavonol structures may differentially modulate antioxidant defence. Di- and trihydroxy flavonols may synergise with POD, while trihydroxy flavonols appear to compete with the ascorbate-APX system. This coordinated response indicates an active role for flavonols under UV radiation. They may modulate enzymatic antioxidant systems through complex, structure-dependent mechanisms. By integrating metabolic, enzymatic, and gene expression data under realistic field conditions, this study provides novel insights into the physiological mechanisms underlying UV acclimation in grapevines. These findings offer a scientific basis for developing viticultural strategies aimed at improving berry quality and enhancing vineyard sustainability under changing climatic conditions.