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.

ブドウ‘ピオーネ’について，休眠の導入と覚醒の過程における芽の生理的変化を調査した．休眠導入期の8月から覚醒初期の12月まで露地で栽培されている個体から芽を採取し，呼吸量，エチレン生成量および含水率を測定し た．調査期間を通して呼吸量は低く，エチレンもほとんど検出されなかった．芽の含水率は8月から10月まで僅かに上昇し，その後は変化がみられなかった．休眠覚醒初期の12月から発芽期の4月中旬まで，芽の呼吸量とエチレン生成量を測定した．呼吸量は4月上旬までは低く推移し，発芽（4月13日）の直前に急上昇した．エチレンは測定期間を通して低かった．休眠期の12月，1月および2月に採取した穂木を2% H2CN2 または蒸留水（対照）で処理し，25℃以上に保ったプラスチックハウスに入れて発芽を調査するとともに，経時的に芽の呼吸量，エチレン生成量および含水率を測定した．両時期とも対照区よりも H2CN2 処理区の発芽が早く，しかも休眠の深い12月処理で区による差が大きかった．両区いずれの時期とも，芽の呼吸量は発芽直前に急上昇したのに対し，エチレン生成量は調査期間を通して低いままであった．芽の含水率は，いずれの時期および処理区とも発芽期に低下し，特に H2CN2 処理区の低下が大きかった．休眠最深期の10月に採取した穂木に ACC，GSH（還元型グルタチオン）および GSSG（酸化型グルタチオン）を処理し，発芽に及ぼす影響を調査したところ，ACC だけが発芽を促進した．同様に，4種のシアン化合物（CaCN2，H2CN2，KCN，NaCN）を処理したところ，H2CN2を除き有意に発芽を促した．これらの結果を基に，ブドウの発芽と生理的変化との関係および休眠覚醒に及ぼすエチレン生合成関連物質の作用性について考察した．