Figure 7
Water flux in roots. (a) The time course of isotopic flux into and out of maize root cells in vivo. Spectra similar to those of Figure 6 were recorded for the 2H signals from D2O that was added to the perfusing medium (J. Bennett, F.Q. and H.J.B., unpublished results). The intensity of the intracellular 2H peak is plotted as a function of time. The high time resolution and sensitivity of the measurements, as well as the fact that the complete time course is recorded from one sample, allows detailed kinetic analysis. (b) Simple model from which the solid line in (a) can be generated. The model is anatomically based and consists of 12 cell layers including exodermal and endodermal layers. There are three independent parameters representing resistances to water movement between cell layers and across the exoderm and endoderm. The model is mathematically simple, being a set of linear flux equations linking successive cell layers and governed by first-order kinetics (Fick's law).