ELICITOR-INDUCED SECONDARY METABOLISM IN RUTA-GRAVEOLENS L - ROLE OF CHORISMATE UTILIZING ENZYMES

In vitro cultures of Ruta graveolens L. respond with rapid accumulatio n of acridone epoxides, furoquinolines and furanocoumarins, when chall enged with autoclaved homogenate of the yeast Rhodotorula rubra. A tra nsient increase of several enzymes of the respective biosynthetic path ways was measured but we still look for the key regulatory enzymes. We investigated whether the branch point enzymes of the shikimic acid pa thway anthranilate synthase (AS) and chorismate mutase (CM) possibly p lay such a role. The two enzymes compete for chorismate. AS forms anth ranilate, the precursor amino acid of acridone and furoquinoline alkal oids. CM channels chorismate into phenylalanine, tyrosine and phenylpr opanoid biosynthesis. Elicitation resulted in a transient increase of the activity of both enzymes. Relative induction rates were 2-4 fold f or AS and about 1.5 fold for CM. Constitutive CM activity, however, is about 1000 fold higher than AS activity. As in other plants 2 isoform s of CM are expected to be present in R. graveolens. A differential de termination of the activity of the isoforms via the tryptophan activat ion rate proved to be ambiguous. Some evidence for the specific induct ion of a plastidic form of CM was obtained by inhibition of translatio n. The time courses of CM induction show CM not to be a key enzyme in elicitor induction of furanocoumarin accumulation. In comparison to ot her enzyme activities induction of anthranilate synthase activity corr esponds closest to inducible acridone epoxide accumulation indicating a key role in its regulation. Induction of AS and CM was inhibited by actinomycin D and chloramphenicol while cycloheximid inhibited AS indu ction only.