Induction of competence for elicitation of defense responses in cucumber hypocotyls requires proteasome activity

• Published in: The Plant journal : for cell and molecular biology Vol. 21; no. 3; pp. 311 - 316
• Main Authors: Becker, Jürgen, Kempf, Ralf, Jeblick, Wolfgang, Kauss, Heinrich
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Science Ltd 01.02.2000; Blackwell Science
• Subjects: Adenosine Triphosphatases - metabolism; Biological and medical sciences; Chitinases - genetics; Cucumis sativus - growth & development; Cysteine Endopeptidases - metabolism; Cysteine Proteinase Inhibitors - pharmacology; Darkness; Fundamental and applied biological sciences. Psychology; Generalities. Disease free stocks; Growth Inhibitors - pharmacology; Hydrogen Peroxide - pharmacology; Hypocotyl - drug effects; Hypocotyl - enzymology; Hypocotyl - growth & development; Lactones - pharmacology; Leupeptins - pharmacology; Light; Multienzyme Complexes - metabolism; Phytopathology. Animal pests. Plant and forest protection; Proteasome Endopeptidase Complex; RNA, Messenger - genetics; Chitinase; Ubiquitin; Multicatalytic endopeptidase complex; Enzyme; Induction; Cucurbitaceae; Cucumis sativus; Peptidases; Signal transduction; Regulation(control); Hypocotyl; Vegetable crop; Dicotyledones; Glycosidases; Angiospermae; Hydrolases; Defense mechanism; Spermatophyta; Elicitation; O-Glycosidases
• ISSN: 0960-7412; 1365-313X
• DOI: 10.1046/j.1365-313x.2000.00677.x

Summary The epidermal cells of hypocotyls from etiolated cucumber seedlings are not constitutively competent for elicitation of the rapid H2O2 defense response. However, elicitor competence developed while conditioning the surface‐abraded seedlings by rotating them in buffer for 4 h. Competence development was greatly potentiated by inducers of systemic acquired resistance and suppressed by specific inhibitors of proteasome activity, clasto‐lactacystin β‐lactone (LAC) and carboxybenzoyl‐ l‐leucyl‐ l‐leucyl‐ l‐leucinal (LLL). In the freshly abraded seedlings, chitinase gene activation became evident approximately 4 h after elicitor addition. Accumulation of chitinase mRNA was enhanced upon conditioning prior to elicitation and was inhibited by LAC and LLL, indicating that the process which leads to H2O2 elicitation competence is also superimposed on the elicitation of chitinase mRNA. LAC and LLL caused an accumulation of ubiquitin‐conjugated proteins and enhanced the expression of a proteasome α‐subunit, suggesting that proteasome activity was specifically inhibited and that the effect observed on gene expression was not due to impaired gene induction in general. Together, our results suggest that the ubiquitin–proteasome system may play a crucial role in a process which switches the signaling pathway for diverse plant defense responses into a functional state, as is known for many basic cellular processes in both animals and yeast.