Abstract
SummaryRadioactive abscisic acid (ABA) was applied to leaves of potted grapevines (Vitis vinifera L.). During a 24‐h experimental period, the ABA was extensively metabolized within the leaf to phaseic acid (PA), 4′‐dihydrophaseic acid (DPA) and abscisyl‐β‐D‐glucopyranoside (ABAGE), together with a number of unknown metabolites. ABA was transported out of the leaf to the roots. The major metabolite in roots was DPA and, 24 h after application of ABA to the leaves, only 5% of the radioactivity in the roots was present as ABA. Very little ABAGE was formed by roots. Xylem sap, expressed from canes or collected by root pressure exudation, also contained labelled material, a high proportion of which was unmetabolized ABA.It is suggested that export of ABA from leaves to roots and subsequent transport back to the leaves via the xylem occur naturally in unstressed grapevines and that this forms an integral part of the stomatal control mechanism.
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