The physiology of bud dormancy and cell cycle status in grapevine

Evaluating the cell cycle status during dormancy of multicellular organisms is problematic. This is particularly so for woody perennial buds, where dormant and quiescent states are diffuse, and the organ may remain visibly unchanged for six to nine months of the year. In this study, we investigate cell cycle status of dormant grapevine buds by measuring mitotic index using an optimised method developed for grapevine bud tissue. The experimental material showed a dynamic range in the depth of dormancy, declining from 200 days in March to less than 60 days in May and 30 days in August, measured as the time to reach 50% bud burst in forcing conditions. Despite these differences, flow cytometry analysis showed that most nuclei isolated from these buds were arrested at the G1 phase. Ultrastructure analysis of the cells in the region of the shoot apical meristem confirmed that the mitotic activities of buds remained low at all time points, together with the development of starch grains and the relative absence of organelle development. HIGHLIGHT The cell cycle and ultrastructure data suggest interesting evidence correspond to the growth resumption capacity of grapevine cv. Cabernet Sauvignon buds, i.e., absence of mitosis activities regardless of dormancy depth and starch accumulation irrespective of chilling accumulation. ### Competing Interest Statement The authors have declared no competing interest. * SAM : shoot apical meristem CZ : central zone PZ : peripheral zone RZ : rib zone LP : leaf primordia BB50 : 50% of bud to burst EL4 : Eichorn-Lorenz scale 4 H2CN2 : hydrogen cyanamide FCM : flow cytometry NIB : nuclei isolation buffer PI : propidium iodide CV : coefficient of variance DF : debris factor TEM : transmission electron microscopy