Stilbene accumulation in grapevine tissues: Developmental and environmental effects

Vitis vinifera L. cvs. Chardonnay and Merlot shoot cuttings with one inflorescence, either with or without leaves were incubated in the glasshouse. Stilbene phytoalexin synthesis in inflorescences was elicited using yeast extract and phenolic compounds in the flowers were analyzed by HPLC. Quercetin derivatives, caffeyl- and coumaryltartaric acids were the main phenolic components in flowers. Trans-resveratrol was the only stilbene measurable in Chardonnay, while up to seven stilbenic compounds including piceid were found in Merlot. Leaf removal drastically reduced the formation of stilbenes and other phenolics. Since Botrytis cinerea can infect flowers and remain latent inside the developing berry until veraison, a decline in stilbene production potential during bloom may increase primary infections of grapes. The decrease in synthesis of flavonoids and cinnamic acid derivatives may enhance the grapes' susceptibility to damaging UV-B radiation and sunburn. V. vinifera cv. Cabernet Sauvignon callus was elicited with UV irradiation. Only young, actively growing callus was capable of producing resveratrol, piceid, epsilon-viniferin, and an unidentified stilbene, whereas old callus had lost this ability. This is similar to the response observed in ripening grape berries, which progressively lose their potential for stilbene synthesis towards fruit maturity. Resveratrol and epsilon-viniferin were only detected in trace amounts in non-irradiated callus, while piceid was present as a constitutive compound. All stilbenes accumulated simultaneously after UV exposure. This indicates that elicitation did not result in release of resveratrol from previously formed piceid, but rather resveratrol was partly glucosilated following de novo synthesis. A slight browning of the callus after UV exposure, indicating oxidation reactions, suggests that epsilon-viniferin synthesis may have been a result of cell damage caused by short-wavelength UV radiation.