Changes in the Endogenous Content and Gene Expression of Salicylic Acid Correlate with Grapevine Bud Dormancy Release

Abstract

The accumulation of cold temperature is an important factor for the release of bud dormancy in grapevine. The stress generated by cold is related to changes in defense hormones such as salicylic acid (SA). To understand the participation of this hormone during grapevine bud dormancy release, in this study, we evaluated the effects of cold accumulation on the endogenous SA content and expression patterns of the synthesis and signaling genes of SA as well as budbreak rates. Buds were subjected to an accumulation of 900 or 600 chilling units (CUs). The budbreak percentage was determined when cold-treated buds were transferred to warm temperatures (25 °C). The percentage of budbreak was closely correlated with the amount of cumulative CUs; the percentage increased gradually with the amount of chilling applied before forcing. The increase in the expression level of the SA biosynthesis gene (ICS2) and the endogenous SA content were quantified in cold-treated buds, and the expression was correlated with the percentage of budbreak. These findings may indicate that in dormant grapevine buds, cold accumulation stimulates the synthesis of SA. In cold-treated buds, the cellular levels of SA led to the expression of the NPR1 and PR1 genes, which was mediated by the transcription factor WRKY70. In contrast, expression of NPR1 and PR1 in control buds, which maintained a basal level of SA, and expression of ICS2 and WRKY70 were not detected, suggesting that the constitutive expression of NPR1-SA is independent. Taken together, the results of this study suggest a possible involvement of the SA signaling pathway in grapevine bud dormancy release.