Organically Bound Deuterium in Rice and Soybean After Exposure to Heavy Water Vapor as a Substitute for Tritiated Water

Heavy water vapor release experiments were carried out in a greenhouse using deuterium as a substitute for tritium and uptake and loss kinetics of D₂O in leaves and formation, translocation and retention of organically bound deuterium (OBD) in rice and soybean were investigated. Rate constants of D₂O uptake in leaves of rice plant and soybean in the daytime release were 2.4 and 3.0 hr⁻¹, respectively, and 5-4 times higher than those in the nighttime release. Rate constants of D₂O loss in leaves after daytime release were about twice those after the nighttime release. The half time of D₂O loss was 0.6–0.7 hr for leaves of rice plant and soybean. After D₂O release, OBD concentration in unhulled rice and soybean increased with time until 4 –5 days of the experiments and then decreased with time and the extent of decrease was remarkable in soybean pea.