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.
Identification of Vitis vinifera L. grape berry skin color mutants and polyphenolic profile