LIGHT EMITTING DIODE IRRADIATION AT NIGHT ACCELERATES ANTHOCYANIN ACCUMULATION IN GRAPE SKIN

We investigated whether irradiating grape bunches with light-emitting diodes (LEDs) at night would enhance anthocyanin accumulation in grape skin. The total anthocyanin contents were significantly higher in irradiation treatments with blue or red LED than in the control, and the effect was significantly stronger with blue LED. Quantitative real-time PCR analysis showed that cumulative daily expression levels of MYB transcription factor genes and anthocyanin biosynthesis pathway genes were higher in the LED irradiation treatments than in the control. These findings suggest that LED irradiation at night enhances the expression of anthocyanin biosynthesis-related genes, and accelerates anthocyanin accumulation. On the other hand, diurnal expression analysis showed that the expressions were low during daytime for both MYB and anthocyanin biosynthesis-related genes when air temperature was high, while the expression levels were high during night for MYB and in the morning for anthocyanin biosynthesis pathway genes when air temperature was low. Therefore, their expressions could also be affected by the ambient temperature. All these results suggest that the increase of anthocyanin contents by LED treatments at night occurred under an environmental condition (low temperature) which favors the expression of anthocyanin biosynthesis-related genes.