Solar UV-B and ABA Are Involved in Phenol Metabolism of Vitis vinifera L. Increasing Biosynthesis of Berry Skin Polyphenols

It has been previously found that abscisic acid (ABA) participates in the activation of grapevine leaf tissue defense against potentially damaging effects of solar ultraviolet-B radiation (UV-B), apparently by triggering biosynthesis of phenols that filter the harmful radiation and act as antioxidants. The present work studies the effect of solar UV-B and exogenously applied ABA on berry growth, sugar accumulation, and phenol (anthocyanin and nonanthocyanin) profiles across berry development and ripening of Vitis vinifera L. cv. Malbec in a vineyard at 1450 m of altitude. The grapevines were exposed to relatively high UV-B irradiation (normal sunlight; +UV-B) and also to a reduced UV-B treatment (filter exclusion; -UV-B). These two UV-B treatments were combined with weekly spray applications to the leaves and berries of 1 mM ABA (+ABA) or H2O (-ABA). Reduction of UV-B delayed berry development and maturation, whereas the +UV-B and +ABA combined treatment hastened berry sugar and phenol accumulation. +UV-B/+ABA treatments also reduced berry growth and decreased sugar per berry without affecting sugar concentration (degrees Brix) at harvest. Berry skin ABA levels were higher in the +UV-B and +ABA combined treatment, which also hastened the onset of ripening up to 20 days. Berry skin ABA levels then decreased toward harvest, implying a possible role for ABA in the control of ripening in this nonclimacteric fruit. Under both +UV-B and +ABA treatments berry skin phenols were additively increased with a change in anthocyanin and nonanthocyanin profiles and increases in the proportion of phenols with high antioxidant capacity.