Auxin Transport in Explants of Coleus

alpha-Naphthaleneacetic acid-C(14), labeled in the carboxyl group, was applied in blocks of agar to the distal and to the proximal (either apical or basal) ends of explants of Coleus. The radioactivity in receiver blocks at the opposite ends was measured. Acropetal transport was slight, only 4% of the basipetal transport.Translocation of NAA-C(14) was polar in basipetal direction. Only 1.4% of the radioactivity lost from donor blocks at the apical position reached the receiver blocks; the greatest part remained in the tissue and was immobilized there. All activity found in 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, so far as the transport of NAA is concerned.