XIII Simposio Hispano-Portugués de Relaciones Hídricas en las Plantas

Abstract

The effect of water stress on grape berry ripening and quality has been extensively investigated during the last decades (Chaves et al., 2010; Lovisolo et al., 2010; Kuhn et al., 2013, Zarrouk et al., 2016). Overall, berry quality benefits from mild to moderate water deficit and the conventional wisdom says that the observed positive effects of water deficits are due to low yield and small berries. But more recently water deficit was shown to profoundly alter berry secondary metabolism, particularly of flavonoids, thus greatly regulating the ripening process. The regulation of genes and proteins of the various metabolic pathways is either the consequence of a direct effect of water shortage and/or indirect via the changing of the light environment around grape clusters due to the impairment of vine vegetative growth. The matter is far from being conclusively addressed and two major causes can be highlighted: the experimental set-ups adopted in the majority of experiments, namely the water stress timing and conditions (pre- or post-véraison water stress); and the diversity of varieties (Zarrouk et al., 2016). Grape berries are non-climacteric fruits wherein abscisic acid (ABA) is central to the ripening process. The differential increase of anthocyanin compounds in berries under pre- or post-véraison deficit irrigation is primarily attributed to large differences in abscisic acid (ABA) sensitivity displayed by different varieties as a consequence of large differences in the ability to regulate water losses through chemical (i.e. ABA) signaling. Grape berries thus represent a unique situation in which abiotic stress and developmental signaling intersect via the activities of ABA. In addition, climate condition, namely high temperature along the growing season is considered a putative constraint to the implementation and success of the deficit irrigation regime. Also the interaction elevated temperature – water deficit is considered as the main cause of complexity of field experiments results namely in what concerns the ripening of wine grapes. During the last ten years, our investigation aimed to comprehend the impact of water stress and heat stress on grape berry ripening, skin secondary metabolism as well as cuticle properties. We have investigated ABA-mediated cross talk between abiotic stress and ripening as it relates to flavonoid biosynthesis in the grape berry skin. We show that the mild

XIII Simposio Hispano-Portugués de Relaciones Hídricas en las Plantas: Pamplona 18-20 Octubre 2016

7 stress imposed by deficit irrigation have a positive impact on berry composition only when high temperature is not a limiting factor. We also show that the biological function of ABA is under berry developmental control and does not correlate with vine water status or berry temperature until a certain water stress threshold. It also appears that ABA catabolism/conjugation processes are implicated in the ripening process and in water and heat stresses responses. In addition, our most recent results in cuticle indicate that water and heat stresses increase berry wax accumulation across berry development, affecting cuticle morphology, composition and transpiration. The recent data related to metabolic changes and hormonal control of grape berry ripening as well as berry cuticle properties under deficit irrigation will be discussed and limitations in the interpretation of results will be identified.