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 expressi ng tryptophan decarboxylase cDNA (tdc) from Catharanthus roseus(l.) G. Don under the control of the CaMV 35S promoter and terminator exhibit ed tryptophan decarboxylase (TDC) enzyme activity and accumulated tryp tamine. The plants with the highest TDC activity contained 19 pkat per mg of protein. The influence of transgenic expression of tdc on the a ctivities of anthranilate synthase (AS) and chorismate mutase (CM) wer e examined in 10 transgenic tobacco plants. The specific activities of these two chorismate-utilizing enzymes were not significantly affecte d by expression of tdc, despite their important functions as branch po int enzymes in the shikimate pathway. The results indicate that the no rmal route of tryptophan biosynthesis in plants is sufficient to suppl y a considerable amount of this essential amino acid for the biosynthe sis of secondary metabolites. Despite their increased tryptamine conte nt, the growth and development of the transgenic tobacco plants expres sing tdc appeared normal.