PROBLEM TO BE SOLVED: To provide the subject new gene coding for a protein having a specific amino acid sequence and exhibiting L-galactonolactone dehydrogenase activity and giving a variety having high vitamin C content by introducing into vegetables such as tomato or potato. SOLUTION: This new gene codes for a protein composed of the amino acid sequence expressed by the formula or a protein composed of the amino acid sequence of the formula provided that one or several amino acids are depleted, substituted or added and having L-galactonolactone dehydrogenase activity. It codes for an enzyme enabling dehydrogenative oxidation of L- galactonolactone to form L-ascorbic acid (reduced-type vitamin C). A vegetable having high vitamin C content and resistant to stress such as oxygen injury can be produced by introducing an expression plasmid integrated with the gene into a vegetable. The gene can be produced by the PCR of the cDNA originated from the root tuber of sweet potato with a primer composed of a partial gene of the above enzyme by conventional method.
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