Effect of applied and endogenous indol-3-yl-acetic acid on maize root growth

The level of endogenous Indol-3-yl-acetic acid (IAA) measured by gas chromatography-mass spectrometry in the elongating zone of intact primary roots of Zea mays showed a good linear correlation with the growth rate of these roots. When they were treated with IAA, their relative elongation decreased; this indicates a supraoptimal content of endogenous IAA. However, the growth of some of the relatively rapidly extending roots was enhanced by such treatment. Interactions between endogenous and applied IAA in the control of root growth are discussed.