Regulatory Mechanism of Anthocyanin Biosynthesis in 'Kyoho' Grape Berries Grown under Different Temperature Conditions

To clarify the mechanism regulating anthocyanin biosynthesis in 'Kyoho' grape berries grown under high temperature, we examined flavonoids accumulation and the activities of related enzymes as well as photoassimilates translocation on the berries. Anthocyanin content in the skin of berries of grape was lowered at 30 days after veraison when grown under high temperature condition (at consistently 30°C) as compared with berries at consistently 25°C or 30°C in the day and 15°C in the night concomitantly. Phenylalanine concentration in the skin and the photoassimilates partitioning to berry were also lower in those grown at 30°C than vines at 25°C or 30/15°C. While, phenylalanine ammonia lyase (PAL) activity in berries grown at 25°C was higher than that in berries grown at 30°C or 30/15°C. Berries grown at 30/15°C had the highest UDP-glucose : flavonoid 3-O-glucosyltransferase (UFGT) activity among three temperature conditions 30 days after veraison. These results suggest that grape berries grown at successive high temperature decrease anthocyanin accumulation in the skin by virtue of the decrease of the UFGT activities and the concentration of phenylalanine and photoassimilates partitioning to berry. On one hand, the grape berry grown under cool night temperature condition would result in high level of anthocyanin accumulation due possibly to great induction of UFGT activity and high phenylalanine accumulation.