It was demonstrated that salicylic acid (SA) not only binds to catalase from differentiated higher plants and plant cell suspension cultures but also to those of fungi and animals. SA bound specifically to iron-containing enzymes, such as catalase, aconitase, lipoxidase and peroxidase, while not to iron-free plant enzymes. On the grounds of these experiments, the claim is further challenged that SA is a signalling compound and second messenger in plants that activates plant defense-related genes through elevated H202 levels by specifically inhibiting catalase activity. SA may just function as a phytoalexin.

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A new enzyme, (S)-norlaudanosoline synthase, which catalyses the synthesis of (S)-norlaudanosoline from dopamine and 3,4-dihydroxyphenylacetaldehyde was isolated from the soluble protein extract of ESCHSCHOLTZIA TENUIFOLIA cell suspension cultures and purified approximately 40-fold. The apparent molecular weight of the enzyme is 15 500 Dalton. The pH optimum is 7.8, temperature optimum 40 degrees C, apparent K (M) values for dopamine and dihydroxyphenyl-acetaldehyde are 1.5 mM and 0.7 mM respectively. The synthase shows high substrate specificity in that only the phenylacetaldehydes are transformed but not the phenylpyruvates. No apparent cofactor requirement could be demonstrated. By means of isoelectric focusing and disc-gel electrophoresis evidence was obtained for the existence of four norlaudanosoline synthase isoenzymes, none of which catalyses the reaction of dopamine with 3,4-dihydroxyphenylpyruvate. These enzymes are responsible for the synthesis of (S)-norlaudanosoline, the key intermediate in the formation of isoquinoline alkaloids occurring in the plant kingdom.

The differential incorporation of doubly labelled strictosidine and vincoside into several indole alkaloids belonging to the Corynanthe (3a and 3p series), Aspidosperma, and lboga types in three plant families has been studied, and it has been demonstrated that only strictosidine is incorporated while vincoside is metabolically inert in these plants with regard to alkaloid formation. During the conversion of strictosidine into the 3P-indole alkaloids, the hydrogen atom at the 3-position is lost, while it is retained during the biosynthesis of the 32 alkaloids. The chemical synthesis of [7-3H]secologanin, an important intermediate for further work in the biosynthesis of monoterpenoid alkaloids, is also described. as a variety of other species in cell cultures by in vivo and in vitro t e c h n i q u e~.~J~ The crucial enzyme catalysing the condensation of (1) with (2) to yield exclusively the a-epimer strictosidine (3) has been discovered and which was shown to be biologically rearranged to the diverse structures of the indole alkaloids found in nature.2 Chemical condensation of (1) and (2) yields a mixture of the two epimers strictosidine (3) and vincoside

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