Chemisch Induzierte Resistenz im Pathosystem Weizen – Echter Weizenmehltau: Cytologische und molekulare Funktionsanalyse eines Benzothiadiazols
Abstract
The natural phenomenon of systemic induced resistance (SIR) is mimicked by application
of the chemical BTH (benzo[1,2,3]thiadiazole-7-carbothioic acid S-methyl ester,
acibenzolar-S-methyl) or other functional analogues of salicylic acid. Chemically Induced
Resistance (CIR) in plants leads to a long lasting protection against a broad range of
phytopathogens. How chemically induced plants respond to pathogens is not well
understood. Here, defence mechanisms were analysed on the cytological, biochemical and
molecular level in the pathosystem wheat - wheat powdery mildew fungus. As a result of CIR the basal resistance is increased. Wheat plants treated with BTH showed
a more frequent formation of effective penetration barriers (papillae) and a hypersensitive
reaction upon pathogen attack. BTH treatment leads to expression of a set of genes partly with unknown function. Some
of these genes are used as marker genes for CIR, since they are expressed specifically after
application of chemical resistance inductors. Temporal and spatial expression patterns of
four chemically induced genes were studied. Comparing different types of chemical
application in combination with inoculation of Bgt, conclusions regarding the importance
of these genes in defence or signal transduction could be drawn. WCI-3 and PR1 appeared to be involved directly in pathogen defence because they show
similarities to antifungal proteins and are expressed in cells at the frontline between plant
and fungus. In western analyses, a priming effect for PR1 was demonstrated. This implies,
that PR1 was expressed in chemically induced plants that were challenged by Bgt-inoculation
stronger and earlier than in control plants which may contribute to
effectiveness of defence. WCI-1 and LOX are genes that might be involved in signal
transduction after BTH application. This is likely for WCI-1, because it was expressed
rapidly and directly at the site of inductor application. Interestingly, LOX was expressed
independent of the type of application, in cells of the vascular bundle sheath and the
adjacent mesophyll. Therefore, the lipoxygenase might be a key enzyme engaged in local
or systemic signal processing.
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