A phytohormone (abbreviation ABA, outdated Dormin) discovered in the 1950s, which has a growth-regulating effect in plants in interaction with auxins, cytokinins and gibberellins. This substance cancels the effect of the growth-promoting hormones and causes, among other things, bud dormancy in already lignified perennial plants. In vines, it is involved in leaf fall, shoot stunting, growth retardation and during grape ripening. During budbreak, the concentration in the buds drops dramatically. Conversely, ABA levels in the newly established winter buds increase in parallel with seed and fruit formation to induce winter bud dormancy. During so-called water stress, the level in leaf tissue increases enormously, because ABA controls the movement of the stomata (sphincter cells, leaf pores) through which the plant releases water (transpiration) and takes up carbon dioxide.