Fatty acid hydroperoxide lyase (HL) is the key enzyme for the production of the "green note"compounds, leaf aldehyde [(2E)-hexenal] and leaf alcohol [(3Z)-hexenol], in plant tissues. A cDNA encoding HL was cloned from leaves of watermelon (Citrullus lanatus) and expressed in Nicotiana tabacum. The enzyme is 3 times more active with 13-hydroperoxylinolenic acid than with 13-hydroperoxylinoleic acid. The activity against 9-hydroperoxides of polyunsaturated fatty acids is minimal. Enzyme activity of the watermelon HL in the transgenic leaves was approximately 50 times higher than endogenous HL activity in the wild-type N. tabacum plants. When compared with Arabidopsis HL also expressed in N. tabacum, the highest HL activity is 10 times higher in watermelon HL overexpressing leaves than in Arabidopsis HL overexpressers.