High temperature at veraison inhibits anthocyanin biosynthesis in berry skins during ripening in 'Kyoho' grapevines

We examined the effects of high temperature (HT) at veraison (the onset of ripening) on coloration and anthocyanin biosynthesis in berry skins of 'Kyoho' grapevines (Vitis labruscana L.). The vines were subjected to control, HT (6 °C higher than the control for 10 days), and intermittent HT (IHT; 6 °C higher than the control for 4 days followed by control temperature for 3 days and then 6 °C higher than the control for another 3 days) conditions from 50 to 60 days after full bloom (DAFB) in temperature-controlled rooms. Under control conditions, berry skins were tinted purple from 55 DAFB and turned to reddish-purple thereafter until 80 DAFB, concurrently with the anthocyanin accumulation. The HT and IHT treatments greatly inhibited the coloration and anthocyanin accumulation, with greater inhibition by the HT treatment. The HT and IHT treatments significantly inhibited the expressions of early (EBGs) and late anthocyanin biosynthetic genes (LBGs), and the transcription factor gene VlMYBA2. Abscisic acid (ABA) contents in the control berry skins increased from 50 DAFB, peaked at 55 DAFB, and decreased thereafter. The HT and IHT treatments reduced the increase in ABA contents, with no significant difference between HT- and IHT-treated vines. Gibberellin (GA) contents decreased during veraison in the berry skins of control and IHT-treated vines, but remained unchanged in those of HT-treated vines. These results suggest that the coloration and anthocyanin biosynthesis in berry skins are associated with changes in the ABA/GA ratio.