CUTIN MONOMERS AND SURFACE WAX CONSTITUENTS ELICIT H2O2 IN CONDITIONED CUCUMBER HYPOCOTYL SEGMENTS AND ENHANCE THE ACTIVITY OF OTHER H2O2 ELICITORS

Hypocotyls from etiolated cucumber (Cucumis sativus L.) seedlings were gently abraded at their epidermal surface and cut segments were condi tioned to develop competence for H2O2 elicitation. Alkaline hydrolysat es of cutin from cucumber, tomato, and apple elicited H2O2 in such con ditioned segments. The most active constituent of cucumber cutin was i dentified as dodecan-1-ol, a novel cutin monomer capable of forming hy drophobic terminal chains. Additionally, the cutin hydrolysates enhanc ed the activity of a fungal H2O2 elicitor, similar to cucumber surface wax, which contained newly identified alkan-1,3-diols. The specificit y of elicitor and enhancement activity was further elaborated using so me pure model compounds. Certain saturated hydroxy fatty acids were po tent H2O2 elicitors as well as enhancers. Some unsaturated epoxy and h ydroxy fatty acids were also excellent H2O2 elicitors but inhibited th e fungal elicitor activity. Short-chain alkanols exhibited good elicit or and enhancer activity, whereas longer-chain alkan-1-ols were barely active. The enhancement effect was also observed for H2O2 elicitation by ergosterol and chitosan. The physiological significance of these o bservations might be that once the cuticle is degraded by fungal cutin ase, the cutin monomers may act as H2O2 elicitors. Corrosion of cutin may also bring surface wax constituents in contact with protoplasts an d enhance elicitation.