Root-Pressure Exudation in Woody Plants

A study was made of differences in amount and concentration of root-pressure exudate from detopped root systems of several woody species. Root-pressure exudation was exhibited by young grape plants and young seedlings of tulip tree, birch, and red maple but not by loblolly pine, white spruce, and sugar maple. The salt concentration of the root-pressure exudate was always greater than that of the external solution. When solution was pushed through the root systems by applying a pressure of 1 arm to the solution surrounding the roots, the volume of exudate increased considerably and its salt concentration decreased. Nevertheless, the total amount of salt delivered per unit of time increased. Completely suberized root systems of dormant grape plants exhibited copious exudation when detopped. Their response to detopping and to application of pressure to the solution surrounding the roots was, qualitatively, very similar to that of actively growing grape root systems. Root-pressure exudation was manifested by individual, excised, actively growing, white root tips from all seven species. An increase in solution temperature from 24⚬ to 34⚬ C increased the yield of exudate from individual roots of pine and spruce more than seven times. The rate of exudation from single roots of grape and white spruce was decreased by sodium azide. Individual excised roots of loblolly pine that were completely Suberized exhibited considerable exudation. In fact, after a 24-hr lag, the rate of exudation from these roots began to increase rapidly, soon surpassing the exudation rate from actively growing roots. Removal of the epidermal layer from unsuberized grape roots appeared to increase root-pressure exudation.