Microautoradiographic investigations on bidirectional translocation in the phloem of Vicia faba.

Using radioactive phenylalanine as a tracer, bidirectional translocation in the phloem of a single stem bundle of Vicia faba L. was detected by analyses of microautoradiographs. Bidirectional translocation occurred in lateral leaf traces subtending a leaf of a certain developmental stage. Before and after this stage, translocation was unidirectional, either acropetal or basipetal, respectively.