IMPACT OF ABSCISIC ACID ON THE METABOLISM OF PHENOLIC COMPOUNDS IN GRAPE SKINS: MODULATION OF ANTHOCYANIN AND TANNIN ACCUMULATION THROUGHOUT GROWTH

Abstract

Tannins and anthocyanins are crucial compounds for grape and wine quality. The understanding of their biosynhesis is still in progress and the elucidation of the mechanisms controlling their metabolism would be a determining tool for improving grape maturation. To date, the involvement of abscisic acid (ABA) in anthocyanin accumulation has been widely described, but little is known about the impact of this growth regulator on tannins. Our work aimed to assess the impact of ABA on tannins and anthocyanins accumulated in grape skin, following a precocious treatment of grape with ABA. The skin contents in free ABA and phenolic compounds were measured, which made it possible to validate the hormonal changes induced by the treatment and to show a change in the time-course of accumulation of both tannins and anthocyanins. We then focused on the synthesis of these compounds via expression and enzymatic studies and demonstrated that ABA affected tannin and anthocyanin in an opposite pattern, in accordance with the change in contents: ABA decreased gene expression of structural genes as well as enzyme activity related to tannin production during the 1 st growth period, while it increased gene expression and enzyme activity related to anthocyanin at the time of colour-change. These results showed a direct effect of ABA on both tannin and anthocyanin biosynthesis in grape skins. .