Bunch Shading During Different Developmental Stages Affects the Phenolic Biosynthesis in Berry Skins of 'Cabernet Sauvignon' Grapes

The effect of bunch shading during early development (before the onset of ripening),and/or during ripening on the phenolic composition of grape skins (Vitis vinifera L. cv. Cabernet Sauvignon) as well as on the mRNA levels of the biosynthetic genes on the flavonoid pathway was examined. Shading during early development resulted in decreased proanthocyanidin (PA) concentrations. The PA concentrations decreased during ripening, and the decrease of the concentrations was lower in berries shaded during early development than that in the exposed berries. Thus. no significant effect of shading during early development was observed at harvest. Shading during ripening, did not influence this decline in thee PAs. On the other hand, shading during early development induced changes in the composition such as a decrease of the trihydroxylated subunits within PAs, which agreed with the relative decrease of VvF3'5'H expression. The anthocyanin concentrations were remarkably reduced when the bunches were shaded during ripening, which was in accordance with the decreased transcription of several anthocyanin biosynthetic genes and transcriptional factors. Shading during early development did not influence the anthocyanin concentrations at harvest, however, it decreased the proportion of trihydroxylated anthocyanins. Thus. shading during early development also had an influence on the compounds biosynthesized during ripening.