Water Permeability and Cold Hardiness of Cortex Cells in Cornus stolonifera Michx.—A Preliminary Report

The relationship of freezing resistance to water permeability of cortex cells was studied in stems of red osier dogwood (Cornus stolonifera Michx.). Permeability was estimated by determining the diffusion flux of tritiated water from cortex slices previously equilibrated in tritiated water. Energy of activation and diffusion time comparisons of tritiated water flux from living cortex slices and slices killed by immersion in liquid N(2) verified that intact membranes of uninjured cortex cells limited water flux.Water permeability of living phloem and cortical parenchyma cells increased during the initial (photoperiodically induced) phase of cold acclimation. This accompanied an increase in hardiness from -3 to -12 C. Little if any further increase in permeability was noted during subsequent acclimation to below -65 C.Permeability measurements on nonhardy cortex samples yielded consistent results, but measurements on samples from hardy twigs were often difficult to reproduce. This unexplained variability precludes specific conclusions, but the tritiated water diffusion flux technique may provide an alternative to traditional plasmolytic techniques in studying water permeability in woody plant tissues.