Individual and combined effects of CaCl₂ and UV-C on the biosynthesis of resveratrols in grape leaves and berry skins.

The individual and combined effects of calcium chloride (CaCl2) and ultraviolet C (UV-C) light on the synthesis of resveratrol in grape leaves and berry skins were investigated. Results showed that all treatments could increase leaf resveratrol contents at least about 5 times, but the combination treatment was the most efficient. Moreover, compared with UV-C treatment, the combination treatment delayed the decline of resveratrol contents. The expression levels of phenylalanine ammonia lyase (PAL), cinnamate-4-hydroxylase (C4H), coumaroyl-CoA ligase (4CL), and stilbene synthase (STS) and 3-O-β-glycosyltransferases, which are related to the synthesis of resveratrol, increased in response to these treatments, paralleling the change in resveratrol content. All treatments also induced the biosynthesis of resveratrol in berry skins at room temperature. The berries of these treatments held at room temperature for 1 day were further stored under low temperature (-1 ± 0.5 °C, RH 95%) for 27 days, and the results showed that all treatments continuously increased berry skin resveratrol content, with the combination treatment being most efficient. During cold storage, resveratrol content remained at high levels and reached a maximum (about 247.7 μg/g FW) at 13 days, then showed a slight decline, though it remained high by the end of storage. Berry firmness and total soluble solids content showed slight changes during cold storage, but there were no differences among the treatments. Thus, the combination treatment of CaCl2 and UV-C could be an efficient method for increasing resveratrol content of table grapes during storage under low temperature. This would be potentially beneficial for producing functional fruits.