Abstract

The molecular regulation of stilbene phytoalexin biosynthesis in developing Vitis vinifera L. grape berries was investigated using a UV induction system. Berries were collected at 1, 5, 10 and 16 weeks post-flowering from the cultivars Shiraz, Semillon, Cabernet Sauvignon and Chardonnay and the skins analysed for resveratrol production following irradiation with UV-C light. The rate and maximal level of resveratrol accumulation increased markedly in berries sampled from 1–5 weeks post-flowering and then dramatically declined in maturing berries sampled from 10–16 weeks post-flowering in all cultivars. In berries sampled at 1 and 5 weeks post-flowering, maximal levels of resveratrol accumulation were recorded at incubation periods of 24 and 48 h respectively whereas maximal resveratrol levels were not recorded in week 16 berry skins until 72 h after UV-treatment. Gene expression analysis indicated that stilbene synthase (STS) mRNA accumulated within 4–8 h of UV treatment in berries sampled at 1 and 5 weeks post-flowering, but did not increase in week 16 berries until 24–48 h following UV-irradiation. Furthermore, the overall level of STS gene expression declined in berries sampled 10–16 weeks post-flowering. The results demonstrate that inducible stilbene accumulation in ripening grape berries is highly regulated at the level of STS gene transcription. This decline in inducible STS gene expression may be a major factor contributing to the increased susceptibility of ripening grape berries to Botrytis cinerea infection.