Abscisic acid, carbohydrates, and nitrogen contents of Kyoho grapevines in relation to budbreak induction by water stress

A physiological explanation for the promotive effects of water stress on budbreak and fruitfulness of Kyoho grapevines was sought by determining the contents of abscisic acid, fructose, glucose, inositol, sucrose, starch and soluble, insoluble and total nitrogen in leaf, cane, trunk and root at the end of water stress treatments and budbreak stage. Abscisic acid content increased in response to water stress and decreased upon rewatering to levels comparable to those of unstressed vines, an indication that bud growth inhibition by the initial increase in ABA, if any, was not a long-term one. Sugar contents of water-stressed vines were greater than those of unstressed vines at the end of treatments, indicating a readily available energy source that might play a role in budbreak enhancement upon rewatering. Nitrogen contents of cane, trunk and root increased under water stress at the expense of leaf, indicating accumulation of nitrogen reserves in the vine's permanent organs, and whose remobilization upon rewatering might play a role in promoting budbreak and subsequent growth of the new shoots.