Hydrogen isotope effect on transport of potassium ion in rice seedlings equilibrated with deuterium oxide.

Potassium absorption by the root of rice seedlings, equilibrated with D2O before K+-absorption, decreased proportionally with D2O concentration and the translocation of the absorbed cations by roots to shoots decreased markedly above 40% D2O. An inhibition curve for the absorption process drawn as a relative rate vs. D2O concentration exhibits no threshold in concentration of D2O. While K+-absorption of the seedlings unequilibrated with D2O did not change up to 60% D2O and decreased above 80%. The concentration of D2O of root tissue water reached a balance with the external concentration within 30 min, but the concentration of shoot water required 5-6 h to balance with the external. The concentration of both root and shoot water did not coincide with the external. The suppressive effect of D2O on potassium absorption links not only to D/H ratio in root water but also in shoot water.