Hormonal regulation of apical dominance in soybeans

Abstract

Hormonal regulation of apical dominance in soybeans is dependent on the physiological stage of the lateral buds. In 7-day-old plants the cotyledonary buds are in an active state of mitosis and the application of a single hormone, gibberellic acid (GA) is effective in releasing the buds whilst indole acetic acid (IAA) is ineffective in inhibiting the buds of decapitated plants. In 16-day-old plants in which mitosis in the cotyledonary buds had ceased, a combination of both benzyladenine (BA) and GA was required for bud growth. BA initiated mitosis and GA promoted elongation. Application of IAA to the apical cut surface of these plants was effective in maintaining the inhibition of cotyledonary buds, and this inhibition could be overcome by a direct application of BA and GA to the inhibited buds. This study has shown that the growth of the inhibited cotyledonary buds in soybeans is regulated not only by auxins but by an interaction between auxins, cytokinins, and gibberellins. The effectiveness of any one of these hormones in inhibiting or promoting growth of the buds is dependent on the age of the plant.