Ultraviolet A-specific induction of anthocyanin biosynthesis and PAL expression in tomato (Solanum lycopersicum L.)

Ultraviolet A (UV-A) is an environmental stimulus, and UV-A-induced anthocyanin biosynthesis has been previously investigated in the tomato plant (Solanum lycopersicum L.). UV-A induced anthocyanin biosynthesis in tomato seedlings and co-irradiation with visible light and UV-A did not influence the content of UV-A-induced anthocyanin accumulation. UV-A irradiation induced significant accumulations of anthocyanin in both the cotyledons and hypocotyls of tomato seedlings. Anthocyanin production increased gradually in the tomato hypocotyls after exposure to UV-A and reached maximum levels at 12 h. In the cotyledons, anthocyanin accumulation was significantly increased at 1 h after UV-A exposure and was reduced afterward; however, it increased again beginning at 3 h. The expression of the phenylalanine ammonia-lyase (SlPAL5) gene was shown to be increased after UV-A exposure in a time-dependent manner. UV-A irradiation was also shown to induce anthocyanin accumulation in the epidermis of the tomato fruit; however, SlPAL5 transcripts were detected only at 3 and 24 h after UV-A treatment. After a 1 h pulse of UV-A, SlPAL5 transcripts were increased significantly in tomato cotyledons and hypocotyls after transfer to dark conditions for a short time.