Effects of Irradiance and Copper on the Activity of Ascorbate Oxidase in Detached Rice Leaves

The effects of copper on the activity of ascorbic acid oxidasc (AAO) in detached rice leaves under both light and dark conditions and in etiolated rice seedlings were investigated. CuSO4 increased AAO activity in detached rice leaves in both light and darkness, however, the induction in darkness was higher than in the light. In the absence of CuSO4, irradiance (40 (mu)mol m-2 s-1) resulted in a higher activity of AAO in detached rice leaves than dark treatment. Both CuSO4 and CuCl2 increased AAO activity in detached rice leaves, indicating that AAO is activated by Cu. Sulfate salts of Mg, Mn, Zn and Fe were ineffective in activating AAO in detached leaves. CuSO4 was also observed to increase AAO activity in the roots but not in shoots of etiolated rice seedlings.