1.4.16
INDUCTION OF SYSTEMIC ACQUIRED RESISTANCE IN CUCUMBER BY BENZOTHIADIAZOLE

J DOMMES, C BOVIE, S KAISER, C POIRIER, M EUGENE and D EVERS

Laboratory of Plant Molecular Biology, Department of Plant Biology, B-22, University of Liege, B-4000 Liege, Belgium

Background and objectives
Plants possess different defence mechanisms against pathogenic microorganisms, including both constitutive and inducible ones. Systemic acquired resistance (SAR) is induced after a first contact with an incompatible pathogen; it is a state of relative and non- specific immunity observed in all parts of the plant and lasting for several weeks or even longer. The signal transduction pathway leading to SAR is largely unknown. It has been shown that an accumulation of salicylic acid in systemic tissues is an obligate step [1]. Exogenous application of salicylic acid and of different analogues can induce SAR. In addition to being obvious options for protection of crops against diseases, these chemicals provide opportunities for dissection of the SAR transduction pathway. Amongst the SAR chemical activators, benzothiadiazoles proved very effective in wheat, in tobacco and in Arabidopsis thaliana [2]. The aim of this work was to optimize a system for SAR induction in cucumber and to clone proteins involved in the transduction pathway through mRNA-PCR differential display.

Results and conclusions
Cucumber plants were sprayed with benzo (1,2,3) thiadiazole-7- carbothioic acid S-methyl ester (BTH). The induction of SAR was checked first by challenging treated plants with tobacco necrosis virus (TNV). The induction of pathogenesis-related (PR) proteins of the PR-8 family was also evaluated by Northern hybridization. Treatment with BTH effectively protected the plants against TNV and induced the expression of PR-8 proteins even at concentrations as low as 5 ÁM. Compared to salicylic acid treatment, BTH proved to be a more potent activator of PR-8 gene expression.

To identify genes involved in the transduction pathway activated by BTH, mRNAs were extracted from treated and non-treated plants. They were analysed by PCR-differential display. Several PCR products showing reproducible differential expression are now being cloned. The state of advancement of this work will be presented and discussed.

References
1. Vernooij B, Friedrich L, Morse A et al., 1994. Plant Cell 6, 959-965.
2. Gorlach J, Volrath S, Knauf-Beiter G et al., 1996. Plant Cell 8, 629-643.