The influence of shoots, roots, and hormones on the distribution of leucine, phosphate, and benzyladenine

The problem studied was the control of the relative distribution of metabolites to the shoots and roots. The movement of radioactivity applied as leucine, phosphate, or benzyladenine (BA) was followed in small regenerated bean plants in which the distribution of radioactive sucrose had been previously studied. Removal of either the shoots or the roots greatly reduced the transport of radioactivity in their direction. Auxin and BA partially replaced the growing regions, but their effects were in no way specific to the parts of the plant in which they are naturally formed. Radioactivity from BA, in contrast to the other substances which were studied, moved preferentially towards the shoots and not the roots. The results indicate that the relations between growing shoot and roots involve a direct hormonal interaction. The sinks which develop in response to the hormones may have some specificity in terms of the substances they require or produce and whose transport they influence.