Investigating the effects of temperature on secondary metabolism in Vitis vinifera L. cv. merlot berries

Graduation date: 2010Grapes (e.g. Vitis vinifera L.) are one of the more important fruit crops from an economic standpoint with world market values over 550 million US dollars in 2007 and 2008, second to apples (United States Department of Agriculture). While a satisfactory level of ripeness is of primary concern, the quality of wine grapes is determined the contribution of secondary metabolites. econdary metabolites provide the color, aroma, flavor, and tactile sensations associated with wine and are believed to be of biological value to humans. Anthocyanins provide the color to red grapes and wine while flavonols are thought to provide color stability to wine through copigmentation with anthocyanins. Proanthocyanidins (PAs) provide astringency or a tactile response in the mouth, which is a primary element of wine quality. For the\ud plant, secondary metabolites are involved in signaling, seed dissemination, and protection against biotic and abiotic stresses.\ud In this work, the temperature of field-grown grapes, Vitis vinifera L. cv. Merlot, was manipulated by cooling and heating berries relative to ambient temperatures during three growing seasons. A range of thermal time was investigated by delivering cold air during the day (Cool) or warm air at night (Heat).\ud Additionally, the effect of reducing the diurnal temperature range (DTR) was investigated by daytime cooling and nighttime heating without a significant change in the accumulated thermal time compared to ambient berries. The impact on PAs was studied by imposing treatments from fruit set to véraison during active PA\ud biosynthesis. Treatments imposed from véraison to harvest maturity (≥ 22.0°Brix) were intended to assess the impact on flavonol and anthocyanin accumulation and changes in PAs during ripening. In 2008, experiments focused on PA accumulation by examining metabolites and the expression of genes involved in PA biosynthesis at ten-day intervals up to véraison. \ud Treatment effects described here demonstrate a complex response of grape berries to shifts in temperatures. The data suggest periods of sensitivity with respect to secondary metabolism that may dictate the response to changes in temperatures.\ud To the authors’ knowledge, the data presented here is the first of it’s kind; examining the effect of temperature on active PA biosynthesis in both the skin and seed of grape as well as the effect of altering the DTR of berries grown under field conditions. This research has implications in understanding fundamental plant responses to their environment and the impact of climate shifts and seasonal temperature variations on grape berry composition