Accumulation of ammonium in rice leaves in response to excess cadmium.

The relationship between ammonium accumulation and senescence of detached rice leaves caused by excess cadmium (Cd) was investigated. CdCl(2) was effective in increasing ammonium content in detached rice leaves under both light and dark conditions. Both CdCl(2) and CdSO(4) induced ammonium accumulation in detached rice leaves, indicating that ammonium accumulation is induced by Cd ions. CdCl(2)-promoted senescence and ammonium accumulation is not specific for the rice cultivar used in this study. The senescence of detached rice leaves induced by CdCl(2) was found to be prior to ammonium accumulation. CdCl(2) induces more ammonium accumulation in the dark than in the light. However, CdCl(2) treatment was found to be less effective in promoting senescence in the dark than in the light. The current results suggest that ammonium accumulation is not associated with the senescence of detached rice leaves induced by Cd. Evidence was presented to show that CdCl(2)-induced ammonium accumulation in detached rice leaves is attributed to a decrease in glutamine synthetase (GS) activity.