Article ID: UTD-046
Phytohormones play major roles in the berry maturation process. Gibberellic acid (GA) and cytokinin (CK) are phytohormones used in seedless table grape production. Several studies have been conducted on the effects of GA and CK application on berry development. However, the detailed mechanisms underlying their physiological effects on berry maturation after the veraison stage have not been clarified. Skin browning during maturation is a major commercial problem in yellow-green skinned grape cultivars including ‘Shine Muscat’, and expanding our knowledge of these mechanisms is a necessary step towards addressing this problem. In this study, we investigated the effects of GA and CK treatments from the veraison stage to the subsequent developmental stages of this grape berry. Both treatments resulted in enlarged berries and the suppression of increases in sugar content. Chlorophyll in the berry skin was less decomposed after GA/CK treatment, and the occurrence of skin browning in the maturation stage was reduced, as expression of the VvPP2Cs gene decreased. GA/CK treatment at the veraison stage (45–50 DAFB) reduced the expression levels of phytohormone-related genes, particularly those of VvGID1 and VvCHKs, which are involved in GA and CK signaling, respectively. These similar changes in gene expression patterns suggest phytohormonal crosstalk and a common expressional regulatory mechanism. VvACO2 and VvYUC1 expressions were significantly increased in skin browning samples, regardless of treatment, indicating involvement of the ethylene and auxin biosynthesis pathways in skin browning. Therefore, GA/CK treatment at the veraison stage may broadly affect phytohormone biosynthesis and signaling pathways in subsequent developmental stages, although the effect size greatly differs depending on the experimental conditions, including year and plant.
