Cucumber Hypocotyls Respond to Cutin Monomers via Both an Inducible and a Constitutive H2O2-Generating System1

Abstract

Hypocotyls from etiolated cucumber (Cucumis sativa L.) seedlings were gently abraded at their surface to allow permeation of elicitors. Segments from freshly abraded hypocotyls were only barely competent for H(2)O(2) elicitation with fungal elicitor or hydroxy fatty acids (classical cutin monomers). However, elicitation competence developed subsequent to abrasion, reaching an optimum after about 4 h. This process was potentiated in seedlings displaying acquired resistance to Colletotrichum lagenarium due to root pretreatment with 2,6-dichloroisonicotinic acid or a benzothiadiazole. Induction of competence depended on protein synthesis and could be effected not only by surface abrasion, but also by fungal spore germination on the epidermal surface or by rotating the seedlings in buffer. Inhibitor studies indicated that the inducible mechanism for H(2)O(2) production involves protein phosphorylation, Ca(2+) influx, and NAD(P)H oxidase. In contrast, a novel cucumber cutin monomer, dodecan-1-ol, also elicited H(2)O(2) in freshly abraded hypocotyls without previous competence induction. This finding suggests the presence of an additional H(2)O(2)-generating system that is constitutive. It is insensitive to inhibitors and has, in addition, a different specificity for alkanols. Thus, dodecan-1-ol might initiate defense before the inducible H(2)O(2)-generating system becomes effective.

Silica deposition by a strongly cationic proline‐rich protein from systemically resistant cucumber plants

“…Under the latter condition, no obvious decrease of p8 was observed, indicating that it could still become solubilized by the SDS buffer. Similar results (data not shown) were found when seedlings with surface-abraded hypocotyls received 1 mM H 2 O 2 , four times in the course of a 1-h incubation period, or were supplied for 1 h with 50 mM 1-dodecanol, an elicitor capable of H 2 O 2 production in the etiolated cucumber hypocotyls (Kauss et al, 1999). These results suggest that p8 did not become oxidatively cross-linked, at least in the etiolated cucumber hypocotyls.…”

“…All these treatments are known to be associated with SAR induction and papillae formation (Kauss et al, 1999;Schmele and Kauss, 1990;Siegrist et al, 1994). Thus, there is a strong correlation between PRP1 expression and pathogen defense.…”

“…It was found that in this tissue, chemical SAR induction causes full resistance against Colletotrichum lagenarium. For instance, in control seedlings, the epidermal cell wall of the hypocotyls was penetrated beneath 61 AE 11% of the fungal appressoria, whereas after BTH pre-treatment at the roots, effective papillae were formed and the penetration rate decreased to 1 AE 2% (Kauss et al, 1999).…”

“…Etiolated cucumber seedlings were grown for 4 days, either on water (susceptible) or on a solution of the SAR-inducing chemical (resistant), as described previously (Kä stner et al, 1998;Kauss et al, 1999;Siegrist et al, 1994). In the experiments where exogenous water-soluble substances were applied, the hypocotyl surface was gently abraded with a suspension of SiC to make the cuticle permeable (Kä stner et al, 1998).…”

The Formation and Function of Plant Cuticles

“…The cutin monomers that are released during polymeric cutin hydrolysis can act as elicitors of plant defense responses and are thus classified as damage-associated molecular patterns. At micromolar concentrations, these compounds induce the production of hydrogen peroxide and other defense responses (Schweizer et al, 1996;Kauss et al, 1999). However, the mechanism of plant perception of free cutin monomers is currently unknown (Boller and Felix, 2009).…”