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

Changes in the level of hydrogen peroxide (H2O2) is a good indicator to monitor fluctuations in cellular metabolism and in the stress responses. In this study, the changes in H2O2 content during bud endodormancy (ED) and budbreak were analysed in grapevine (Vitis vinifera L.). The results showed a gradual increase in the H2O2 content during the development of bud ED, which was mainly due to an increase in the activity of peroxidases (PODs). The maximum H2O2 content reached in the grapevine buds coincided with the maximum depth of bud ED. In contrast, during budbreak, the H2O2 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 H2O2 on the expression of genes involved in CK and auxin metabolism was analysed. The results showed that H2O2 represses the expression of the CK biosynthesis genes VvIPT3a and VvLOG1 and induces the expression of the CK-inactivating gene VvCKX3, thus reducing potentially the CK content in the grapevine bud. On the other hand, H2O2 induced the expression of the auxin biosynthesis genes VvAMI1 and VvYUC3 and of the auxin transporter gene VvPIN3, thus increasing potentially the auxin content and auxin transport in grapevine buds. In general, the results suggest that H2O2 in grapevine buds is associated with the depth of ED and negatively regulates its budbreak.

Induction and overcoming of dormancy of grapevine buds in response to thermal variations in the winter period

ABSTRACT: This study quantified the chilling requirements for the induction and overcoming of endodormancy (chilling-controlled physiological dormancy) of grapevines buds. Cuttings of the cultivars Chardonnay, Merlot and Cabernet Sauvignon were collected in vineyards in Veranópolis-RS in the winter period of 2019 and 2020. The cuttings were kept at a constant temperature of 7.2 °C or daily cycles of 7.2/18 °C for 6/18 h, 12/12 h or 18/6 h, up to 600 chilling hours (CH). Every 50 CH, part of the cuttings from each treatment was transferred to a temperature of 25 °C for daily assessment of the budburst in the green tip stage. The cultivars had different chilling requirements for inducing and overcoming endodormancy, reaching a total of 150 CH for ‘Chardonnay’, 300 CH for ‘Merlot’ and 400 CH for ‘Cabernet Sauvignon’. Of these, 50 CH were required to induce endodormancy in cultivars Chardonnay and Merlot and 100 CH for cultivar Cabernet Sauvignon. Dormancy evolution did not differ between cultivars in response to thermal regimes, with a temperature of 18 °C inert to the accumulation of CH. Precocity and uniformity of budburst were higher after chilling requirements were met during endodormancy for each genotype.