Water channel does not limit evaporation of water from plant cells

Abstract

Evaporation of water from the cell surface of the internode ofChara corallina was not affected by HgCl₂ which is known to inhibit water channels. This makes a sharp contrast to the fact that most of osmotically driven water transport is inhibited by HgCl₂. Also in radish hypocotyls whose epidermis had been peeled off, evaporation of water was not inhibited by HgCl₂, while osmotic water transport was significantly inhibited.

The cell wall tube was prepared by squeezing out the content of theChara internode. The rate of evaporation from the cell wall tube filled with 150 mM KCl was almost equal to that from the living cell. The apparent hydraulic conductivity of the cell calculated from evaporation rate was found to be 1–2×10⁻³ pm s⁻¹ Pa⁻¹ which is about 1/1000 times the hydraulic conductivity of the plasma membrane (L_p) and 1/40 times the L_p under maximal inhibition with HgCl₂.

It is concluded that under the relative humidity of 53–70% the rate of evaporation of water from the cell surface is limited by the rate of evaporation from the cell wall which is so low that the loss of water can be supplemented without delay from the cell interior across the plasma membrane even when water channels are completely closed.