Movement of tritiated water through young citrus plants

Water movement through different organs of 1-2 year old Sour Orange seedlings was studied by using tritium as a tracer injected into the nutrient solution. The activity of the leaf tissue water of plants free to exchange water with the atmosphere reached only 60-70% of the nutrient solution even after long periods exceeding 30 h, whereas in plants exposed to dry air the activity approached equilibrium with the solution. Turnover of water was less rapid in the laminae than in the midveins of the leaves, in both cases the rate being a function of the amount of foliage on the plant. A reduction in transpiration rate effected by plastic covering, silicone coating, or abscisic acid spray was clearly indicated by a lowered level of tritium activity in the plant tissue.