Sprouting of paradormant and endodormant grapevine buds under conditions of forced growth: similarities and differences.

MAIN CONCLUSION: Bud-break assays under forced growth conditions suggest that a drop in ABA content and an increase in sugars are common features in the sprouting of paradormant (PD) and endodormant (ED) grapevine buds. However, increases in cell division and in respiration are unique characteristics of the ED budding. In tropical and subtropical regions where the variations in day length and temperatures are minor throughout the year, the rupture of grapevine buds can be achieved during the current growing season given rise to a double-cropping system annually. However, it is unknown whether the breaking buds are in the paradormancy (PD) or endodormancy (ED) stage. In this study, we compared the breakage of PD and ED buds under conditions of forced growth. To do this, the expression of genes related to the metabolism of phytohormones and sugars, and of relevant physiological functions such as respiration and cell division was analyzed temporally throughout the incubation period in both types of buds. An early fall in the expression of the ABA biosynthesis gene (VvNCED1) and increases in genes related to sugar metabolism and transports were observed during the incubation period in both types of buds. However, while in the PD buds, the genes related to respiration and the cell cycle did not undergo significant changes in their expression during the incubation period, in the ED buds, the expression of these genes together with those related to auxin and cytokinin biosynthesis experienced a large increase. The results suggest that a drop in ABA content and an increase in sugars are early signals for the onset of bud break in both PD and ED vines, while the increase in respiration and cell division are unique characteristics of the ED buds, which reflect its transition from a resting state to a state of active growth.