Studies of Root Function in Zea mays

The volume flux, J(v), and the osmotic driving force, sigma big up tri, openpi, across excised root systems of Zea mays were measued as a function of big up tri, openP, the hydrostatic pressure difference applied across the root, using the pressure jump method previously described (Miller DM 1980 Can J Bot 58: 351-360). J(v) varied from 5.3% to 142% of its value in intact transpiring plants as a result of the application of pressure differences from -2.4 to 2.4 bar. The calculated hydraulic conductivity was 5.9 x 10(-4) cubic centimeters per second per bar per gram 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 J(v) big up tri, openpi, and the xylem solute concentration as a function of big up tri, openP.