On the relation between auxin transport and auxin metabolism in explants of Coleus

Summary Transport and metabolism of naphthylacetic acid, labelled with ¹⁴C or with ³H, were studied by means of the liquid scintillation counting technique in combination with thin layer chromatography.The amounts of radioactivity reaching the receiver blocks as well as the loss from donor blocks greatly depended on the donor concentration. The relative amounts in receiver blocks increased with decreasing auxin concentrations in donor blocks. This phenomenon may be ascribed to the low immobilization capacity of the tissue at very low auxin concentrations.The relative amounts of radioactivity lost from donor blocks increased with decreasing auxin concentrations in donor blocks.Different characteristics of auxin transport can be explained by assuming a movement in symplast or in apoplast. During transport in the symplast the auxin is immobilized. Auxin immobilization governs many characteristics of auxin transport and could have a regulating effect on the free auxin content in plant tissues.