A discovered only in the 1950s Phytohormon (Abbreviation ABA, outdated Dormin), which interacts with plants auxins. cytokinins and gibberellins has a growth-regulating effect. This substance abolishes the effect of the growth-promoting hormones and causes, among other things, in already woody, perennial plants, the bud rest. With vines it is at leaf fall, Shoot dehydration, growth inhibition and during grape ripening involved. During the expulsion the concentration in the buds drops drastically. Conversely, the ABA level in the newly formed winter buds increases in parallel with seed and fruit formation, in order to bring about the wintry bud dormancy. When so-called water stress the proportion in the leaf tissue increases enormously, because ABA controls the movement of the stomata (Guard cells, leaf pores) through which the plant water gives off (transpiration) and carbon dioxide receives.
By Watering tests In Australia, it has been found that dehydration increases the amount of ABA in the leaf tissue and causes the stomata to close, thereby minimizing water loss through transpiration. But with closed stomata no carbon dioxide uptake for sugar production is no longer possible, all lack of water production of all productive processes. The plant stops growing and takes care of it. Targeted metered dehydration can cause a reduction in yield in viticulture, which is at mass media promote quality. However, too strong promotes water stress the appearance of UTA (untypical age tone) in wine and diminishes it storage capacity, See also below grapevine,