A low temperature promotes anthocyanin biosynthesis but does not accelerate endogenous abscisic acid accumulation in red-skinned grapes.

The effect of temperature on the concentrations of anthocyanins and endogenous plant hormones [abscisic acid (ABA), auxin, and cytokinin] were investigated using the detached berries of two related red-skinned cultivars cv. 'Aki Queen' and 'Ruby Roman' of the table grape Vitis labrusca L. × Vitis vinifera L. The total anthocyanin concentration of both cultivars was lower when exposed to high rather than low temperatures after véraison (the onset of ripening). However, the responses to temperature differed between the two cultivars, and anthocyanin accumulation could occur in 'Ruby Roman' at a higher temperature than in 'Aki Queen'. High temperatures increased the expression of VlMybA1-2 and VlMybA1-3, which encode myeloblastosis (MYB)-related transcription factors; however, the expression of the anthocyanin biosynthesis-related structural genes uridine diphosphate-d-glucose: flavonoid 3-O-glucosyltransferase, flavonoid 3'5' hydroxylase, and flavonoid O-methyltransferase at different temperatures did not correspond with that of the expression of MybAs. The concentration of ABA and its derivatives increased under high temperatures, but that of auxin and cytokinin decreased. The observation that high temperatures induced the accumulation of ABA and expression of VlMybA1s but not the expression of anthocyanin biosynthesis-related structural genes implied the operation of a mechanism different from up-regulation of anthocyanin synthesis by VlMybA1s in the temperature response of grape berries.