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The possibility that ammonium (NH4+) accumulation is linked to the senescence of detached rice (Oryza sativa) leaves induced by copper (Cu) was investigated. CuSO4 was effective in promoting senescence of detached rice leaves. Both CuSO4 and CuCl2 induced NH4+ accumulation in detached rice leaves, indicating that NH4+ accumulation is induced by copper. Sulfate salts of Mg, Mn, Zn, and Fe were ineffective in inducing NH4+ accumulation in detached rice leaves. The senescence of detached rice leaves induced by Cu was found to be prior to NH4+ accumulation. Free radical scavengers, such as glutathione and thiourea, inhibited senescence caused by Cu and at the same time inhibited Cu-induced NH4+ accumulation. The current results suggest that NH4+ accumulation is not associated with senescence induced by Cu, but is part of the overall expression of oxidative damage caused by an excess of Cu. Evidence was presented to show that copper-induced ammonium accumulation in detached rice leaves is attributed to a decrease in glutamine synthetase activity and an increase in reduction of nitrate. |
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