A cDNA encoding a cytochrome P450 (CYP76B9) was isolated from Petunia hybrida. Northern blot analysis revealed preferential expression of the gene in flowers and leaves. The recombinant yeast microsomes expressing CYP76B9 was allowed to react with capric acid and lauric acid as substrates. One major metabolite was produced from each fatty acid after incubation with yeast microsomes expressing CYP76B9. The metabolites were identified by gas chromatography-mass spectrometry (GC-MS) as omega-hydroxy capric acid and omega-hydroxy lauric acid. The kinetic parameters of the reactions were Km=9.4 microM and Vmax=13.6 mol min(-1) per mol of P450 for capric acid, and Km=5.7 microM and Vmax=19.1 mol min(-1) per mol of P450 for lauric acid. We found that the omega-hydroxy metabolites of capric acid and lauric acid can affect the plant growth of Arabidopsis thaliana. Plants grown in the presence of omega-hydroxy fatty acids exhibited shorter root length than control plants with the corresponding non-hydroxylated fatty acids.