Physiological Aspects of Bud Associated with　Breaking Dormancy in Grapevines

Changes in CO2 and C2H4 production and water content of bud associated with breaking in ‘Pione’ grapevine (Vitis labrusca ×V. vinifera) were investigated throughout dormancy. Buds were collected monthly from August to December, during dormancy induction and maintenance, and CO2 and C2H4 production were determined by GC after incubation. Both CO2 and C2H4 production, especially for the latter, were low throughout the experiment. Water content of bud gradually increased until October ; thereafter it was constant. When CO2 and C2H4 production was determined from December to April, during dormancy maintenance to release, CO2 production was low from beginning of experiment to early April, prior to bursting, then rapidly increased to April 13, the bursting date. C2H4 production was almost undetectable throughout the experiment. Cuttings obtained at 3 different stages of dormancy were applied with 2% H2CN2 or distilled water (control), and budbreak was monitored in a plastic house kept at 20℃ or more. The CO2 and C2H4 production of bud were also determined weekly until budbreak. Regardless of treatment time H2CN2 significantly promoted budbreak compared to the control. Significantly higher production of CO2 was observed in cuttings treated with H2CN2 at 3 to 9 days before bursting for all the treatment times. C2H4 production was very low throughout the experiment for all the treatments. Irrespective of chemical application and treatment time, water content of bud decreased to the bursting stage, H2CN2 treatment especially showing a large decline. When dormant cuttings were treated with ACC, GSH (reduced glutathione) and GSSG (oxidized glutathione), only ACC promoted budbreak. Budbreak in cuttings treated with cyanamides such as CaCN2 and H2CN2 and cyanides such as KCN and NaCN was significantly accelerated except for H2CN2. Based on these results, the relationship between budbreak of grapevine buds and physiological changes in buds, and the roles of substances related to ethylene biosynthesis on breaking bud dormancy are discussed.