Control of the Biosynthesis of Phenylalanine and Tyrosine in Plant Tissue Cultures: Lack of Repression of Chorismate Mutase.

Tobacco rice, carrot and tomato tissue cultures were grown in liquid media containing L-phenylalanine or L-tyrosine, or both together. The addition of these amino acids increased their respective cellular levels (4-20 fold ), but did not lower the level of chorismate mutase, an enzyme in the biosynthetic pathway of phenylalanine and tyrosine. These results indicate that the biosynthesis of phenylalanine and tyrosine in cultured plant cells is not regulated by repression of the synthesis of chorismate mutase by phenylalanine or tyrosine. The four species of tissue cultures studied here had similar enzyme specific activities four days after inoculation into fresh culture medium: tobacco 0.4, rice 0.5, tomato 0.4 and carrot 0.75 μmol prephenate formed in 30 min per mg protein. [ABSTRACT FROM AUTHOR]