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. CdCl2 was effective in increasing ammonium content in detached rice leaves under both light and dark conditions. Both CdCl2 and CdSO4 induced ammonium accumulation in detached rice leaves, indicating that ammonium accumulation is induced by Cd ions. CdCl2-promoted senescence and ammonium accumulation is not specific for the rice cultivar used in this study. The senescence of detached rice leaves induced by CdCl2 was found to be prior to ammonium accumulation. CdCl2 induces more ammonium accumulation in the dark than in the light. However, CdCl2 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 CdCl2-induced ammonium accumulation in detached rice leaves is attributed to a decrease in glutamine synthetase (GS) activity. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.