Abstract
Plants form various oxylipins as signaling molecules or defense compounds under stress condition. Usually, oxylipins are formed from free fatty acids, and a lipase reaction to release free fatty acids from membrane lipids is thought to be a step regulating the content of oxylipins. However, we found that a part of oxylipins was formed without any lipase actions but directly from lipids at least in Arabidopsis. When Arabidopsis No-0 leaves were homogenized, C6-compounds were formed through hydroperoxide lyase reaction; however, formation of C12-oxo acids was much lower than that expected. When lipids extracted from the disrupted leaves were digested with pancreatin, C12-oxo acids were released, which indicated that some of C12-oxo acids were in their esterified forms. When leaves of Arabidopsis Col-0 that had no hydroperoxide lyase activity were disrupted, formation of arabidopsides was observed. In vitro experiment showed that galactolipids could be the substrates for lipoxygenase, and their hydroperoxides could be the substrates for hydroperoxide lyase. These results suggested that some oxylipins were formed directly from galactolipids without any lipase reactions in Arabidopsis.
