Is Phloem Transport Due to a Hydrostatic Pressure Gradient? Supporting Evidence From Pressure Chamber Experiments

Abstract

A pressure chamber was used to increase suddenly the hydrostatic pressure in the upper shoot of a Phaseolus vulgaris plant while observing phloem transport of ¹¹C-labelled photoassimilate. Phloem transport in the stem towards the chamber stopped immediately when pressure was applied and then recovered within about 5 min. If the pressure was then released, flow increased again. The results support the hypothesis that flow of photoassimilate in the stem phloem was driven by a hydrostatic pressure gradient.