Correlative Bud Inhibition and Abscisic Acid in Acer pseudoplatanus and Syringa vulgaris

Growing shoots of Acer pseudoplatanus and Syringa vulgairs were decapitated and defoliated (“treated”) in June 1972–1975. During the 2–3 weeks after treatment the contents of abscisic acid (ABA) in the out-growing lateral buds at the upper-most node as well as in the petiole stumps and nodes were determined by means of gas-liquid chromatography. The concentration of ABA in lateral buds of intact shoots, calculated on a fresh weight basis, varied greatly from year but was consistently several times higher than in petioles and nodes. Defoliation and decapitation caused out-growth of the lateral buds. This was accompanied by a sharp decrease in the ABA concentration, which finally reached the level of petiole tissue. The concentration of ABA in controls (“untreated”) decreased also, but to a smaller extent, and remained higher than in petioles. In petioles and nodes of treated as well as of untreated shoots, the ABA concentration did not change. The absolute amount of ABA in the buds of treated shoots after 2–3 weeks varied greatly, but was apparently not different from the amount in buds of untreated controls or in buds at the beginning of the experiment. Therefore, the decrease of the ABA concentration was mainly due to fresh weight increase. The results are discussed in relation to a possible role of ABA in correlative bud inhibition.