Lipoxygenase pathway in tulip: biosynthesis of ketols.

The metabolism in vitro of [1-(14)C]linoleate, [1-(14)C]linolenate and their 9(S)-hydroperoxides in tulip (Tulipa gesneriana) was found to be under the control of 9-lipoxygenase and allene oxide synthase, and directed towards alpha-ketol, gamma-ketol and the novel compound (12Z)-10-oxo-11-hydroxy-12-octadecadienoic acid (10,11-ketol). Potent activity of allene oxide cyclase (in bulbs) and a new enzyme, gamma-ketol reductase (in bulbs and leaves), was detected. Metabolism in flowers is directed predominantly towards alpha-ketol hydroperoxide.