EXCESS COPPER INDUCES A CYTOSOLIC CU, ZN-SUPEROXIDE DISMUTASE IN SOYBEAN ROOT

The induction of several proteins in soybean roots in response to copper was investigated. The major Cu2+-induced protein of 16 kDa was purified by SDS-PAGE and 2D-PAGE. This Cu2+-induced protein cross-reacted with antibodies against cytosolic Cu,Zn-SOD and the sequence of 40 amino-terminal residues of this protein was found to be 70% and 62.5% homologous to the sequences of cytosolic Cu,Zn-SOD from rice and tomato, respectively. An assay of enzymatic activity revealed that SOD activity of Cu2+-treated soybean roots was more than twice that in roots of non-treated control plants. Thus, treatment with copper of soybean roots appears to induce an increase in SOD activity via the synthesis of cytosolic Cu,Zn-SOD. The induction of SOD by such treatment may be the result either of a direct effect of copper on the gene for SOD or of an indirect effect via an increase in levels of O2-..