INCREASE OF CINNAMALDEHYDE GROUPS IN LIGNIN OF TRANSGENIC TOBACCO PLANTS CARRYING AN ANTISENSE GENE FOR CINNAMYL ALCOHOL-DEHYDROGENASE

An antisense gene for Aralia cordata cinnamyl alcohol dehydrogenase (CAD) was introduced into tobacco plants, Two transgenic plants showed 55 and 20% reduction of the CAD activity compared to that of the control plant. Lignin content measured by the acetyl bromide method showed no significant differences between these plants and the control plant. However, the content of p-hydroxycinnamaldehyde groups in lignin was higher in the transgenic than in the control plants. The increase of p-hydroxycinnamaldehyde groups correlated inversely with the levels of CAD activity, Phloroglucinol staining of transverse sections of stem internode indicated that the fiber secondary wall reacted more strongly with the reagent in the transgenic plants, These results suggested that suppression of CAD activity in tobacco plants results in an increase of cinnamaldehyde groups in lignin, but no significant change in lignin content.