Grape berry flavonoids: A review of their biochemical responses to high and extreme high temperatures.

Climate change scenarios predict an increase in average temperatures and in the frequency, intensity and length of extreme temperature events in many wine regions around the world. In already warm and hot regions, such changes may compromise grape growing and the production of high quality wine as high temperature has been found to critically affect berry composition. Most recent studies focussing on the sole effect of temperature, separated from light and water, on grape berry composition found that high temperature affects a wide range of metabolites, and in particular flavonoids - key compounds for berry and wine quality. A decrease in total anthocyanins is reported in most cases, and appears to be directly associated with high temperature. Changes in anthocyanin composition, and flavonol and proanthocyanidin responses are less consistent, and reflect the complexity of the underlying biosynthetic pathways and diversity of experimental treatments that have been used in these studies. This review examines the impact of high temperature on the biosynthesis, accumulation and degradation of flavonoids and attempts to reconcile the diversity of responses in relation to the latest understanding of flavonoid chemistry and molecular regulation.