Hormonal interaction in controlling apical dominance in soybeans

Abstract

Growth of cotyledonary buds in soybean plants is controlled by an interaction between hormones and is dependent on age of the plant and meristematic activity of the buds. Indoleacetic acid (IAA) applied to the cut surface of decapitated 7-day-old plants does not inhibit the growth of buds which are actively undergoing mitosis. Growth is inhibited, however, when IAA is applied in combination with benzyl-adenine(BA) and this inhibitory effect is minimized by gibberellic acid (GA). In 16-day-old plants where mitosis in the buds has ceased IAA alone inhibits bud growth. In both 7- and 16-day-old decapitated plants, application of GA, alone or in combination with BA promotes growth of the buds. Inhibited buds have two peroxidase isoenzymes with pronounced activity. The activity of one of these decreases when the buds are released from dominance. Benzyladenine applied directly to inhibited buds initiates growth in 16-day-old intact plants and this growth is further enhanced when GA is applied 48 h after BA treatment. The enhanced growth by GA is prevented if 5-fluorouracil (5-FU) or 5-fluorodeoxyuridine (5-FDU) are applied before but not after the GA treatment. These results indicate that the hormones have a sequential role in releasing buds from apical dominance.