Studies of Root Function in Zea mays

Abstract

The volume flux, Jv and the osmotic driving force, .sigma..DELTA..pi., across excised root systems of Z. mays were measured as a function of .DELTA.P, the hydrostatic pressure difference applied across the root, using the pressure jump method previously described (Miller, 1980). Jv varied from 5.3-142% of its value in intact transpiring plants as a result of the application of pressure difference from -2.4 to 2.4 bar. The calculated in hydraulic conductivity was 5.9 x 10-4 cm3 s-1 bar-1 g-1 root and was independent of pressure. A model of root function similar to those appearing in the literature failed to provide quantitative accord with the data. A proposed model, which includes the effect of volume flux on the distribution of solutes in the symplasm, predicts accurately Jv .delta..pi., and the xylem solute concentration as a function of .DELTA.P.