Improving antioxidant activity in transgenic Codonopsis lanceolata plants via overexpression of the γ-tocopherol methyltransferase (γ-tmt) gene

Codonopsis lanceolata Trautv (Companulaceae) is a folk medicine in Korea. To shift the content of tocopherol and enhance its antioxidant properties, we overexpressed the gamma-tocopherol methyltransferase (gamma-tmt) gene in C. lanceolata. The antioxidant activity of methanolic crude extracts of the transgenic plants was compared to that of control plants using the 1,1-diphenyl-2-picrylhydrazyl radical scavenging method, with alpha-tocopherol and butylated hydroxy toluene as standard antioxidants. The antioxidant activity of the leaf and root extracts of transgenic plants was higher (IC (50) 12-17.33 and 408-524 mu g/ml, respectively) than that of control plant leaf and root extracts (18 and 529 mu g/ml, respectively). High-performance liquid chromatography analysis of phenolic compounds confirmed an increase in the levels of 12 major phenolic acids and flavonoids in the leaf and root extracts of transgenic plants compared to control plants. We also found that the rate of photosynthesis was 48% higher in transgenic plants than in control plants. Based on these results, we suggest that increases in the alpha-tocopherol level in transgenic C. lanceolata plants may result in increases in the photosynthetic performance and antioxidant metabolism of these plants.