Abstract
In summer shoots of Abies sachalinensis MAST. seedlings, the cytokinin activity at Rƒ 0.1_??_0.2, 0.5_??_0.7 and 0.8_??_1.0 (corresponding to zeatin or zeatin riboside) in paper chromatography by means of bioassays of cucumber cotyledons, was greater, compared with that in buds before summer shoot growth. It also differed from that in opened buds in the spring which had cytokinin activity mainly at Rƒ 0.8_??_1.0. In roots, regarded as a place of cytokinin synthesis, a large amount of cytokinin activity, chiefly at Rƒ 0.9_??_1.0, was observed from June 16 to July 20, while a small amount of it was observed on August 30. Spraying with 250 and 500ppm of 6benzyladenine promoted the summer shoot growth of seedlings remarkably. Spraying with either 500ppm of ethrel or 100ppm of a-naphthaleneacetic acid inhibited such growth. From these results, it is suggested that cytokinins play an important rôle in the promotion of summer shoot growth, and conversely, auxins and ethylene inhibit it.
