3-Hydroxy-3-phenylpropanoic acid is an intermediate in the biosynthesis ofbenzoic add and salicylic acid but benzaldehyde is not

Stable-isotape-labelled (H-2(6), O-18) 3-hydroxy-3-phenylpropanoic acid, a putative intermediate in the biosynthesis of benzoic acid (BA) and salicyli c acid (SA) from cinnamic acid, has been synthesized and administered to cu cumber (Cucumis sativus L.) and Nicotiana attenuata (Torrey). Analysis of t he products by gas chromatography-mass spectrometry revealed incorporation of labelling into BA and SA, but not into benzaldehyde. In a separate exper iment, 3-hydroxy-3-phenylpropanoic acid was found to be a metabolite of phe nylalanine, itself the primary metabolic precursor of BA and SA. These data suggest that cinnamic acid chain shortening is probably achieved by beta - oxidation, and that the proposed "non-axidative" pathway of side-chain degr adation does not function in the biosynthesis of BA and SA, in cucumber and N. attenuata.