RADIOAUTOGRAPHIC STUDY OF TRANSLOCATION IN BEAN LEAVES

The movement of the radioactivity from sucrose, indole-3-acetic acid (IAA) and phosphate has been examined in excised bean leaves. Preferential translocation of the labelled materials toward the base of leaf and petiole was demonstrated, suggesting a natural mobilization gradient down the leaf and petiole. Establishment of other mobilization centers in the leaf by local application of N⁶-benzyladenine diverted the movement of the sucrose label and, to a lesser extent, the phosphate label. There was no apparent mobilization of IAA by benzyladenine. Evidence is provided that there is a continuity of label from the source to the sink regions, and it is suggested that reported instances of noncontinuity of label may be attributable to the refixation of respired C¹⁴O₂ by tissue treated with benzyladenine. The observations appear to substantiate the concept that the unloading of solutes from the phloem can regulate the direction and intensity of translocation.