No abstract

The cell walls of two near-isogenic lines of bean (Phaseolus vulgaris L.) seedlings, susceptible or resistant to the bean anthracnose pathogen Colletotrichum lindemuthianum, were digested with the pure endopolygalacturonase (endoPG; EC 3.2.1.15) isolated from the fungus. The solubilized pectic fragments were separated according to their charge and size. Analysis of their uronic acid contents showed that their elution patterns were quite dissimilar, depending on whether they originated from the resistant or the susceptible host plant. Their sugar compositions revealed that neutral sugars were more abundant in the fragments released from the resistant plant than from the susceptible one, while the reverse was true for acidic residues. The fragments solubilized from the resistant plant induced an increase of pathogenesis-related (PR) proteins when challenged on resistant or susceptible bean seedlings, both at the transcript and enzyme-activity levels. On the other hand, pectic fragments released from susceptible bean cell walls exhibited either no signi®cant activity or only a weak elicitor eect on the defence of susceptible or resistant bean seedlings. The dierential elicitor eect observed between pectic fragments was inversely correlated to their acidity. Thus, endoPG-released pectic fragments from bean cell walls exhibited the same ability as the endoPG itself (C. La®tte et al., 1993, Mol PlantMicrob Interact 6: 628±634) to elicit defence responses in a cultivar-speci®c manner.

Inoculation of different bean cultivars witb Colletotrichum lindemuthianum race jS results in a marked increase of y3-l,3-glucanase and chitinase activities. The increase is mucii faster in incompatible than in compatible interactions. Induced /3-1,3-glucanase (pi 9,5) differs from the constitutive/J-1,3glucanase (pi 4,5) of healthy plants. The induced enzyme can partly degrade, m vitro, the cell walls of C. lindemuthianum. The possible role of these bydrolytic enzymes in plants defence is discussed. ZusammenfassungDie Induktion von /J-1,3-Glukanase-und Chitinaseaktivitat in kompatiblen und nichtkompatiblen Interaktionen zwischen Colletotrickum lindemuthianum und Bohnensorten Nach einer Inokulation von Bohnensorten mit der Rasse /3 von Colletotrichum lindemuthianum wurde eine signifikante Erhohung der /5-1,3-Glukanase-und Chitinaseaktivitat festgestellt. Bei nichtkompatiblen Interaktionen trat die Erhohung schneller ein als bei kompatiblen. Die induzierte /)-l,3-Glukanase (pi 9,3) unterscheidet sich von der konstittitiven P-],3-Glukanase (pi 4,5) gesunder Pflanzen. In •yifro-Untersuchungen zeigten, dall das induzierte Enzym die Zellwande von C. lindemuthianum zum Teil degradieren kann. Die moghche Rolle dieser hydrolytischen Enzyme bei der Pflanzenabwehr wird diskutiert.