The water relations of hemlock (Tsuga canadensis). III. The temperature dependence of water exchange in a pressure bomb

The pressure-bomb technique has been used to measure the temperature dependence of water exchange between the apoplast and symplast of hemlock (Tsuga canadensis) shoots. By applying the Arrhenius rate theory, the activation energy for water exchange in the whole shoot equals 25.9 + 0.6 × 103 J per mole. A theory is proposed on the basis of the Arrhenius rate equations which allows us to predict the relative magnitudes of the membrane resistance, Rm, and the extracellular resistance, Rx, to water permeation. On the basis of our calculations, we believe Rm is at least one-quarter of Rx and may even exceed Rx, but more work needs to be done to be sure.