Auxin Transport in Explants of Coleus

Abstract

Explants of Coleus rhenaltianus, consisting of a node with 0. 5-cm pieces of stem above and below the node and 2 petiole stumps each 0. 5 cm long, were used to measure translocation of the auxin [image]naphthaleneacetic acid in the tissue. [image]Naphthalene acetic acid C14-labelled in the carboxylgroup (NAACl14) was applied at various positions in agar blocks, and the radioactivity in receiver blocks at the opposite ends and in the tissue determined. Translocation of NAAC14 was polar in a basipetal direction. However, a slight acropetal (4% of the basipetal) translocation was found too. Only 1.4% of the radioactivity lost from donor blocks(2. 10-4[image]) at the apical position reached the receiver blocks; the greater part remained in the tissue and was immobilized there. All activity found in the receiver blocks at the basal end appeared to be still in the form of NAA. There were no differences between petiole tissue and stem tissue, as far as the transport of NAA was concerned. Time course of loss of radioactivity from donors was the same for NAAC14 as for sucrose-C14. The velocity of translocation varied between 6. 9 and 7. 5 mm/hour. It is suggested that the entrance from donor block to tissue may be the same for all substances, while polarity is specific for certain compounds and determined by other processes.