Abstract
Cytochrome b561 mediates the trans-membrane transfer of electrons from ascorbate in one side of membrane to monodehydroascorbate in the other side. In the stress-tolerant wild watermelon leaves, mRNA for CLb561-A encoding cytochrome b561 was induced by drought/excess light stresses. Western blotting analysis showed that the CLb561-A protein was undetectable under low light conditions, but accumulated under high light conditions. Moreover, the abundance of the CLb561-A protein was increased significantly by the drought treatment. The GFP fusion assay demonstrated that the CLb561-A protein was localized in the plasma membrane. We also found that the activity of apoplastic ascorbate oxidase in the wild watermelon leaves was more than ten times as high as those in other plants. These observations suggest occurrence of the large electron flow from the cytosol to the apoplastic space, which may contribute to the dissipation of excess energy in wild watermelon.
