Screening Methods for Arabidopsis Mutants Affected in the Signal Transduction Pathways Leading to Defense Responses

In this paper we describe the development of screening methods for Arabidopsis mutants affected in defense responses. Mutants putatively affected in the oxidative burst are being isolated by screening for decreased reactivity of seedlings with nitro blue tetrazolium. Mutants affected in the activation of a rice basic chitinase promoter in transgenic Arabidopsis plants are being selected by allyl alcohol treatment of seedlings after mutagenesis, using the expression of alcohol dehydrogenase controlled by the chitinase promoter. We also describe systemic acquired resistance (SAR) in Arabidopsis, induced by inoculation with an avirulent pathogen. Plants inoculated in this way become systemically protected against a secondary challenge with a virulent strain, showing a HR-like reaction to this strain, which normally would cause disease symptoms. Moreover inoculation with the avirulent strain also results in protection against other bacterial pathogens. A screening method for isolation of mutants affected in SAR is presented.