Cutin Monomers and Surface Wax Constituents Elicit H2O2 in Conditioned Cucumber Hypocotyl Segments and Enhance the Activity of Other H2O2Elicitors1

Abstract

Hypocotyls from etiolated cucumber (Cucumis sativus L.) seedlings were gently abraded at their epidermal surface and cut segments were conditioned to develop competence for H 2 O 2 elicitation. Alkaline hydrolysates of cutin from cucumber, tomato, and apple elicited H 2 O 2 in such conditioned segments. The most active constituent of cucumber cutin was identified as dodecan-1-ol, a novel cutin monomer capable of forming hydrophobic terminal chains. Additionally, the cutin hydrolysates enhanced the activity of a fungal H 2 O 2 elicitor, similar to cucumber surface wax, which contained newly identified alkan-1,3-diols. The specificity of elicitor and enhancement activity was further elaborated using some pure model compounds. Certain saturated hydroxy fatty acids were potent H 2 O 2 elicitors as well as enhancers. Some unsaturated epoxy and hydroxy fatty acids were also excellent H 2 O 2 elicitors but inhibited the fungal elicitor activity. Short-chain alkanols exhibited good elicitor and enhancer activity, whereas longer-chain alkan-1-ols were barely active. The enhancement effect was also observed for H 2 O 2 elicitation by ergosterol and chitosan. The physiological significance of these observations might be that once the cuticle is degraded by fungal cutinase, the cutin monomers may act as H 2 O 2 elicitors. Corrosion of cutin may also bring surface wax constituents in contact with protoplasts and enhance elicitation.

Apoplastic Diffusion Barriers in Arabidopsis

“…Although cutin monomers induce early defense responses in plants, neither a receptor for cutin monomers nor a downstream signal transduction cascade has been identified (Schweizer et al, 1996;Fauth et al, 1998). However, transgenic CUTE plants do not show defense responses that can be specifically attributed to the release of cutin monomers; instead, these responses are due to an increase in cuticle permeability, because the observed phenotypes are similar to those observed in a number of mutants with impaired cutin biosynthesis (Sieber et al, 2000).…”

The Plant Cuticle Is Required for Osmotic Stress Regulation of Abscisic Acid Biosynthesis and Osmotic Stress Tolerance inArabidopsis

“…Interestingly, these mutants are more resistant to the necrotrophic fungus Botrytis cinerea (Bessire et al, 2007;Chassot et al, 2007;Tang et al, 2007), although the mechanisms for this immunity are unknown. Cutin monomers or other constituents of the cuticles could elicit reactive oxygen species production (Fauth et al, 1998) and can potentially serve as signals to activate defense responses in the host. It is known that ABA is actively involved in plant resistance to pathogens (Mauch-Mani and Mauch, 2005;Adie et al, 2007;de Torres-Zabala et al, 2007;Fan et al, 2009); whether reduced ABA biosynthesis in cuticle mutants has a direct role in regulating disease resistance will need to be investigated in the future.…”

The Biopolymers Cutin and Suberin

“…In plants, treatment with exogenous cutinase or cutin monomers lead to resistance of plants to certain pathogens (Namai et al, 1993;Schweizer et al, 1994;1996a). Although the resistance mechanism remains to be elucidated, several experiments demonstrated that cutin monomers are perceived by the plants to induce defense reactions, such as alkalinization of the medium of potato cell cultures and H 2 O 2 production in cucumber hypocotyls (Schweizer et al, 1996b;Fauth et al, 1998;Kauss et al, 1999). Cutin monomers may also contribute to resistance by inhibiting the germination of fungal spores .…”