Exudation, 86Rb transport, and water permeability were examined in excised roots of honey locust (Gkditsia triacanthos L.) treated by removing the tip 2 mm (tip-cut 2 mm) or tip 8 mm of the root, or by adding kinetin, or by both treatments. Tip removal increased the rate of exudation. Kinetin, 5 x 10-6 M, inhibited exudation and Rb transport in tip-cut 2-mm roots; the inhibition was reversible. Kinetin inhibition of exudation was initially associated with lower K(Rb) transport and later with decreases in both ion transport and water permeability. Exudation was also inhibited at 10-10 to 10-7 M kinetin. Exudation from roots with intact tips was not altered by kinetin until after about 24 hours. Light during the exudation period had no significant (95%) influence on rate of exudation during the first 24 hours whether root tips were cut or kinetin applied.The results suggest the involvement of the root tip in regulating exudation in other parts of the root. This regulation might occur through cytokinin control of water permeability and the rate of ion transport. This study examined whether or not kinetin would stimulate K(Rb) transport from media to exudate of excised roots. The localization in or very near the root tip of K or Rb absorption (30) and transport (21, 30), high respiration (17), water uptake (1), and cytokinin occurrence and possibly synthesis (20,26) suggested a possible interaction between cytokinins and K(Rb) absorption and transport. Some studies suggested indirectly that cytokinin would stimulate K transport from media to exudate. These include the following. ABA decreased K and Cl ion transport in barley roots (4). ABA acted opposite to cytokinin in relation to root exudation (24) and stomatal opening (8). Cytokinin stimulated stomate opening (8) and separate work related stomate opening to K ion influx into guard cells (6). No study was found which determined whether the stomatal opening induced by cytokinin was directly related to K ion transport. Kinetin promoted the uptake of K and Rb into detached sunflower cotyledons (10).Other lines of evidence suggest that K transport from media to exudate might be inhibited by cytokinin. The osmotic pressure of root exudate from tomato was increased, but the amount of exudate was decreased by kinetin treatment given for 2 days before root excision in half strength of Hoagland solution (24). Rb uptake by bean stem was inhibited by BA (18). K uptake by beet root disk was also inhibited by BA and kinetin (28 roots, while protein synthesis increased 2-fold (29). Kinetin increased the total ionic concentration of excised corn roots, but decreased rate of exudation and K transport during 24 hr (29). Hong (7) discussed in detail other literature relating cytokinins to exudation and ion transport.To test whether or not kinetin stimulates K ion transport into exudate, the following scheme of experiments was followed. The first experiment compared the rate of exudation in tip-cut and tip-intact roots, since the root tip is a possible site of cytokinin bio...