Effects of Ultraviolet C Irradiation on Stilbene Biosynthesis in Vitis vinifera L. cv. Cabernet Sauvignon Berry Skins and Calli

Vitis vinifera L. cv. Cabernet Sauvignon berries and calli were irradiated with ultraviolet C (UV-C) to
investigate the effects on the biosynthesis of stilbene. The stilbene content in the berry skins was enhanced
significantly after 10 min of UV-C irradiation over the 24 h time course, and the results varied depending
on the development stage of the fruit. The maximum production of total stilbene in the berry skins
occurred at 12 h after treatment, with a content of 848.45 ± 23.53 μg/g fresh weight (FW) at the beginning
of véraison, 591.77 ± 26.90 μg/g FW at the end of véraison, and 170.71 ± 6.85 μg/g FW at the ripening stage.
Different UV-C dosages, from 5 to 30 min, induced stilbene accumulation considerably in the calli over the
120 h experimental period, and 20 min was the most efficient. The maximum of total stilbene accumulation
in the calli was 125.07 ± 3.01 μg/g FW at 96 h after 20 min irradiation. Total phenolics and total flavonoid
content increased after UV-C irradiation in both the berry skins and calli. The relative expression of genes
encoding enzymes involved in the branching point of stilbene and flavonoid biosynthesis was up-regulated
by UV-C irradiation. The results show that UV-C irradiation significantly promotes stilbene and flavonoid
biosynthesis in grape berry skins and calli, and the induction effects depend on fruit development stage
and UV-C dosage.