Effects of Exogenous Factors on Phenylalanine Ammonia-Lyase Activity and Accumulation of Anthocyanins and Total Phenolics in Grape Berries

Abstract

The effects of ethephon (E), sucrose (S), and light (L) on phenylalanine ammonia-lyase (PAL) activity and on the concentration of anthocyanins and total phenolics in the berry skins of Vitis vinifera L. Cardinal berries were studied at temperatures of 14°, 22°, and 35°C over a period of 72 hours. Maximum PAL activity was obtained in the light/ethephon/sucrose-treated (LES) and light/sucrose-treated (LS) berries at 36 and 48 hours. In berries kept in the dark, PAL activity decreased over the experimental period. Anthocyanin concentration increased rapidly after a phase of slow accumulation of 24 to 60 hours, depending on the temperature, in the presence of light but not in the dark. Sucrose plus ethephon had a synergistic effect on synthesis of anthocyanins at 22°C. The period of slow anthocyanin accumulation was shortened as temperature increased. Cycloheximide (CHI) applied to LES-treated berries at 22°C caused a significant reduction in the concentration of anthocyanins in berry skins. Rapid phenolic accumulation in grape berry skins occurred after 48 hours at all temperatures. The pattern of changes in total phenolics in berry skins was similar for all temperature treatments with the maximum concentration reached after 60 hours. There were no consistent effects of sucrose and ethephon on total phenol accumulation in berry skins.