Light-Dependent Ammonium Ion Toxicity of Rice Leaves in Response to Phosphinothricin Treatment
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Ammonium ion accumulation in detached rice leaves treated with phosphinothricin (PPT), an inhibitior of glutamine synthetase (GS), was investigated in the light and darkness. PPT treatment increased NH4+ content and induced toxicity in rice leaves in the light but not in darkness, suggesting the importance of light in PPT-induced NH4+ toxicity in detached rice leaves. PPT treatment in the light resulted in a decrease of activities of the cytosolic form of GS and the chloroplastic form of GS. The photosynthetic electron transport inhibitor 3-(3,4-dichlorophenyl)-1,1-dimethylurea reduced NH4+ accumulation induced by PPT in the light. In darkness, PPT-induced NH4+ accumulation and toxicity were observed in the presence of glucose or sucrose.
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