Changes in the Coloration and Activities of Enzymes Involved in Anthocyanin Synthesis of ‘Kokuo’ Grapes Grown under Different Temperature Conditions During Ripening

Abstract

To clarify the mechanism regulating anthocyanin biosynthesis in ‘Kokuo’ grapes grown under high night temperatures, we examined flavonoid accumulation and the activities of related enzymes in the grapes. When grapes were grown at 25 °C day temperature and high night temperatures (25 °C), anthocyanin content in the skin was higher than that of grapes grown under low night temperatures (15 °C). On the contrary, at 30 °C day temperature conditions, anthocyanin content in the skin of grapes grown under high night temperatures (30 °C) was markedly lower than that of grapes grown under low night temperatures (15 °C). Flavonol and proanthocyanin contents in the skin of grapes grown under high temperatures were higher than that of grapes grown under low night temperatures. Although there was little effect of night temperatures on phenylalanine ammonia lyase (PAL) activity in the skin, UDP-glucose: flavonoid 3-O-glucosyltransferase (UFGT) activity in the skin of grapes grown under high night temperatures was lower than that of grapes grown under low night temperature. These results suggest that anthocyanin accumulation in the skin of grapes grown at continuous high night temperatures is decreased due to decreased UFGT activities.