GROWTH-INHIBITING PROPERTIES OF XYLEM EXUDATE FROM VITIS-VINIFERA

An inhibitory effect on the growth of Lemna minor L. cultures has been demonstrated in xylem exudate from Vitis vinifera L. var. Waltham Cross bled from canes cut near the time of budburst. Most inhibitory activity was detected up to the time of maximal daily exudation, which corresponded closely with budburst. After this time the inhibitory activity rapidly disappeared. A similar pattern occurred in each of the 3 years of the study, 1988-1990. Using ultrafiltration, it was shown that most of the growth inhibitor activity of the crude exudate was located in the 0.5-10 kDa fraction. This fraction exhibited a seasonal variation in its bioactivity similar to that of the crude exudate samples. The 0.5-10 kDa fraction was found to contain abscisic acid but not in a sufficient quantity to account for the inhibitory effects. When chromatographically separated fractions corresponding to oligosaccharides were pooled, biological activity equivalent to that of the crude exudate was retained, which provides evidence that the inhibitor is possibly an oligosaccharide.