ABA Biosynthesis Genes are Down-regulated While Auxin and Cytokinin Biosynthesis Genes are Up-regulated During the Release of Grapevine Buds From Endodormancy

Auxin–cytokinin (CK) interactions have been extensively studied in the control of bud outgrowth in herbaceous plants. However, in temperate woody plants where the meristem of dormant buds can be repressed by either exogenous or endogenous factors, abscisic acid (ABA) has been suggested as a potential regulator of bud outgrowth. To investigate the involvement of ABA, CK, and auxin on bud sprouting in Vitis vinifera , single-bud cuttings were used under forced conditions. This artificial bud sprouting system mimics and hastens the natural sprouting process that occurs in spring. Our results showed that expression of the ABA biosynthesis gene VvNCED1 decreased during incubation, whereas expression of the ABA catabolism gene VvA8H3 remained unaltered. Expression of CK biosynthesis-related genes ISOPENTENYL TRANSFERASE ( VvIPTs ) and LONELY GUY ( VvLOG1 ), CK catabolism-related gene CYTOKININ OXIDASE ( VvCKX3 ), and key auxin biosynthesis gene VvYUC3 increased with incubation time. Moreover, treatment with hydrogen cyanamide (HC), a compound that breaks vine latency, increased expression of VvIPTs and VvLOG1 and reduced expression of VvCKX3 and VvNCED1 . These results are consistent with previous reports indicating that HC increases CK levels and decreases ABA levels in grapevine buds. Taken together, the results suggest that in the vine, bud sprouting is preceded by a decrease in ABA content and an increase in CK and auxin levels.