Impact of diurnal temperature variation on grape berry development, proanthocyanidin accumulation, and the expression of flavonoid pathway genes

To the best of our knowledge, one or more authors of this paper were federal employees when contributing to this work.\ud This is the publisher’s final pdf. The published article is copyrighted by Oxford University Press and can be found at: http://www.oxfordjournals.org/Little is known about the impact of temperature on proanthocyanidin (PA) accumulation in grape skins, despite its\ud significance in berry composition and wine quality. Field-grown grapes (cv. Merlot) were cooled during the day or\ud heated at night by +/–8 C, from fruit set to veraison in three seasons, to determine the effect of temperature on PA\ud accumulation. Total PA content per berry varied only in one year, when PA content was highest in heated berries\ud (1.46 mg berry⁻¹) and lowest in cooled berries (0.97 mg berry⁻¹). In two years, cooling berries resulted in a significant\ud increase in the proportion of (–)-epigallocatechin as an extension subunit. In the third year, rates of berry\ud development, PA accumulation, and the expression levels of several genes involved in flavonoid biosynthesis were\ud assessed. Heating and cooling berries altered the initial rates of PA accumulation, which was correlated strongly\ud with the expression of core genes in the flavonoid pathway. Both heating and cooling altered the rate of berry\ud growth and coloration, and the expression of several structural genes within the flavonoid pathway