Promotion of stem elongation by indole-3-butyric acid in intact plants of Pisum sativum L.

While indole-3-butyric acid (IBA) has been confirmed to be an endogenous fo rm of auxin in peas, and may occur in the shoot tip in a level higher than that of indole-3-acetic acid (IAA), the physiological significance of IBA i n plants remains unclear. Recent evidence suggests that endogenous IAA may play an important role in controlling stem elongation in peas. To analyze t he potential contribution of IBA to stem growth we determined the effective ness of exogenous IBA in stimulating stem elongation in intact light-grown pea seedlings. Aqueous IBA, directly applied to the growing internodes via a cotton wick, was found to be nearly as effective as IAA in inducing stem elongation, even though the action of IBA appeared to be slower than that o f IAA. Apically applied IBA was able to stimulate elongation of the subtend ing internodes, indicating that IBA is transported downwards in the stem ti ssue. The profiles of growth kinetics and distribution suggest that the bas ipetal transport of IBA in the intact plant stem is slower than that of IAA . Following withdrawal of an application, the residual effect of IBA in gro wth stimulation was markedly stronger than that of IAA, which may support t he notion that IBA conjugates can be a better source of free auxin through hydrolysis than IAA conjugates. It is suggested that IBA may serve as a phy siologically active form of auxin in contributing to stem elongation in int act plants.