We have determined the primary structures of two 4-coumarate: CoA ligase (4CL) isoenzymes in parsley (Petroselinum crispum) by sequencing near full-length cDNAs corresponding to the two 4CL genes, Pc4CL-1 and Pc4CL-2, present in this plant. Comparison of the cDNA and genomic nucleotide sequences showed that each 4CL gene is organized in five exons separated by introns of varying lengths. The positions of introns are the same in both genes and 97-99% of the corresponding nucleotide sequences are identical. The two isoenzymes, which are nearly identical in their primary structures, were separated by ion-exchange chromatography, and were found to be indistinguishable with regard to substrate specificity. Assignment to Pc4CL-1 and Pc4CL-2 was achieved by comparison with catalytically active 4CL proteins, isolated from Escherichia coli cells which had been transformed with plasmids harboring the corresponding cDNAs.One active response of plants to environmental stress is the accumulation of secondary metabolites. Many of these plant metabolites are phenylpropanoid derivatives, e.g. flavonoids, isoflavonoids, coumarins, lignin and related phenolic compounds [I, 21. The CoA esters of 4-coumaric and other substituted cinnamic acids are essential intermediates in the biosynthesis of most or all of these compounds. The sequence of reactions leading to the formation of the thiol esters is called general phenylpropanoid metabolism [l] ( Fig.

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Summary Cultured parsley (Petroselinum crispum) cells respond differentially to UV‐containing white light and fungal elicitor. Both stimuli activate the transcription of genes encoding enzymes of partly overlapping phenylpropanoid biosynthetic pathways. Irradiation induces vacuolar accumulation of flavonoids, whereas elicitor treatment stimulates the secretion of furanocoumarins. Simultaneous treatment of parsley cells with UV light and elicitor results in quantitative changes in both responses. Irradiation reduces elicitor‐induced furanocoumarin synthesis, possibly by post‐transcriptional mechanisms, whereas elicitor treatment completely blocks the light‐induced accumulation of flavonoids by repressing the transcription of the chalcone synthase gene. We have identified elicitor‐sensitive regions in the chalcone synthase promoter by transient expression analysis of selected promoter constructs linked to the β‐D‐glucuronidase reporter gene in parsley protoplasts. These regions are identical to those that were found to be sufficient for light inducibility of the chalcone synthase promoter.