Symplasmic transport of water along the root depends on pressure

The gradient NMR method was applied to study intercellular water flows in root segments of maize (Zea mays L.) under disturbance of root hydrodynamic system by the increase in external pressure up to 4 MPa. The rate of intercellular water flows along the root symplast was found to depend on the magnitude and dynamics of pressure changes. Based on the previously predicted cupola-shaped dependency of water flow on the aperture of plasmodesmal neck constrictions, we assume that the external pressure stimulates (via cytosolic calcium) the activity of contractile structures localized in the neck regions of plasmodesmata. Cells of Chlorella vulgaris were taken for comparison since their water relations and cell structure differ strongly from the root cells of maize. The results show that the diffusional water flow in Chlorella is independent of external pressure both in intact cells and in algae, whose plasma membrane was artificially permeabilized.