Hydrogen Peroxide Increases during Endodormancy and Decreases during Budbreak in Grapevine ( L.) Buds.

Changes in the level of hydrogen peroxide (HO) is a good indicator to monitor fluctuations in cellular metabolism and in the stress responses. In this study, the changes in HO content during bud endodormancy (ED) and budbreak were analysed in grapevine ( L.). The results showed a gradual increase in the HO content during the development of bud ED, which was mainly due to an increase in the activity of peroxidases (PODs). The maximum HO content reached in the grapevine buds coincided with the maximum depth of bud ED. In contrast, during budbreak, the HO content decreased. As the plant hormones cytokinin (CK) and auxin play an important role in budbreak and growth resumption in grapevine, the effect of exogenous applications of HO on the expression of genes involved in CK and auxin metabolism was analysed. The results showed that HO represses the expression of the CK biosynthesis genes and and induces the expression of the CK-inactivating gene , thus reducing potentially the CK content in the grapevine bud. On the other hand, HO induced the expression of the auxin biosynthesis genes and and of the auxin transporter gene , thus increasing potentially the auxin content and auxin transport in grapevine buds. In general, the results suggest that HO in grapevine buds is associated with the depth of ED and negatively regulates its budbreak.