Evidence for a Flow of Water into Sieve Tubes Associated with Phloem Loading

Evidence that there is a lateral water flow associated with the loading of sieve tubes is presented. The change in phloem transport dynamics, measured using 11C, induced by leaf anoxia is shown to be consistent with a reduction in lateral water flow brought about by a decline in sucrose loading. The temporal profiles of tracer activity are used to derive a simple holistic model of the phloem pathway which is able to account for the observed dynamics.