ANTHRANILATE SYNTHASE AND CHORISMATE MUTASE ACTIVITIES IN TRANSGENIC TOBACCO PLANTS OVEREXPRESSING TRYPTOPHAN DECARBOXYLASE FROM CATHARANTHUS-ROSEUS

Transgenic Nicotiana tabacum L. 'Petit Havana' SR1 F-1-plants expressing tryptophan decarboxylase cDNA (tdc) from Catharanthus roseus(l.) G. Don under the control of the CaMV 35S promoter and terminator exhibited tryptophan decarboxylase (TDC) enzyme activity and accumulated tryptamine. The plants with the highest TDC activity contained 19 pkat per mg of protein. The influence of transgenic expression of tdc on the activities of anthranilate synthase (AS) and chorismate mutase (CM) were examined in 10 transgenic tobacco plants. The specific activities of these two chorismate-utilizing enzymes were not significantly affected by expression of tdc, despite their important functions as branch point enzymes in the shikimate pathway. The results indicate that the normal route of tryptophan biosynthesis in plants is sufficient to supply a considerable amount of this essential amino acid for the biosynthesis of secondary metabolites. Despite their increased tryptamine content, the growth and development of the transgenic tobacco plants expressing tdc appeared normal.