Biochemical approaches to study the effects of temperature on grape composition in cv. Sangiovese (Vitis vinifera L.).

High temperatures during ripening, especially after veraison, can affect berry composition in wine grapes. In particular, skin anthocyanin accumulation in black varieties can be negatively influenced. The aim of the present research is to evaluate the effects of high temperatures on flavonoids biosynthesis and the mechanisms responsible for low anthocyanin content, often verified in berries ripened in conditions of elevated temperatures. The study was conducted on potted uniform plants of Sangiovese which were kept in two plastic tunnels, from veraison to harvest, with different temperature conditions. In the first one, the berry temperature was maintained below 30o C during ripening (Low Temperature/LT) and in the second tunnel, the temperature was similar to the field conditions (the average and the maximum of berry temperature during ripening were about 25oC and 40oC respectively, High Temperature/HT). Results indicated that no significant differences have been found in total soluble solids (oBrix), pH and titratable acidity concentrations in HT berries as compared to LT; however a tendency to a higher sugar level has been recorded during ripening in the former. In HT the concentration of total anthocyanin of berry skin was significantly lower than in LT. Among the different anthocyanins, malvidin-3-glucoside seems to be less sensitive to high temperature during ripening. PAL activity in the both LT and HT berries increased gradually after veraison, but was significantly lower in HT plants. Using delphinidin and cyanidin as substrates, the activity of UFGT was also strongly reduced in HT plants compared to the LT ones. Independently from thermic conditions, UFGT activity was higher for cyanidin respect to delphinidin and POD activity strongly increased in HT. In conclusion in cv. Sangiovese the interactive effects induced by the reduction of UFGT and PAL and the increase of POD activities may be considered responsible of the lower anthocyanin concentration recorded in HT treatment