Book Description

The aim of the thesis was to assess the effect of UV-B radiation on grapevine Vitis viniferacv. Tempranillo leaf physiology and grape berry composition, framed within the climatechange scenario. Experiments were conducted under glasshouse controlled conditions withfruit-bearing cuttings. Plants were exposed to three UV-B biologically effective doses (0,5.98, 9.66 kJ m-2 d-1) either from fruit set or veraison to maturity. The combined effects of UVand water deficit, as well as, UV-B and elevated CO2-temperature (700ppm, +4oC), appliedfrom fruit set to maturity were also tested. Gas exchange, Chlorophyll a fluorescence, lipidperoxidation, antioxidant enzyme activity, UV-B absorbing compound levels and chlorophylland carotenoid concentration were determined in leaves. Berry development was assessedquantitatively (e.g. elapsed time to reach phenological stages). Amino acid, anthocyanin andflavonol concentrations and profiles were analyzed in berries, as well as, transcript profilingof regulatory and structural genes involved in flavonoid biosynthesis.The results show that initial down-regulation of photosynthesis was followed by anacclimation, mediated by the accumulation of UV-B absorbing compounds and antioxidantresponse elicitation (flavonoids and antioxidant enzymes). Water deficit and elevated CO2-temperature did not alter UV-B acclimation process, however, UV-B did led to certain degreeof cross-tolerance to elevated CO2-temperature, avoiding the senescence-induced oxidativedamage. Berry technological maturity (ca. 22oBrix) was delayed by UV-B exposure and waterdeficit, especially when combined, whereas it was hastened by elevated CO2-temperature. Inthe last case, UV-B attenuated the effect of elevated CO2 and temperature. Changes in berryripening rates were associated with changes in photosynthetic performance.UV-B radiation and water deficit induced lower grape must acidity, mediated by increases inrelative skin mass or potassium levels rather than a decrease in organic acid concentration.In addition this increase in relative skin mass may have contributed to higher anthocyaninconcentration in the must. Grape berry skin flavonol and anthocyanin concentration wasincreased by UV-B, mainly due to the up-regulation of the structural (CHS, F3'H, FLS, UFGTand GST) and regulatory genes (MYBF1 and MYBA1) committed to their synthesis.Quantitative changes in flavonol concentration induced by UV-B were always associated withqualitative changes in flavonol profile (i.e. increased relative abundance of mono- anddisubstituted flavonols), as a result of the competition of FLS with flavonoid hydroxylases(F3'H and F3'5'H) for the same substrates. The independent up-regulation of FLS and F3'5'Hby UV-B radiation and water deficit, respectively, resulted in an intaractive effect on theflavonol B ring hydroxylation pattern. Under elevated CO2-temperature anthocyanin-sugaraccumulation was decoupled. However, UV-B partially alleviated this uncoupling by upregulatinganthocyanin biosynthesis and modulating berry ripening rates.UV-B radiation greatly influenced grapevine leaf physiology and berry composition. Theseresponses to UV-B were modulated, to a greater or lesser extent, by other factors linked toclimate change (water availability, atmospheric CO2 levels and temperature).