Use of new tetrazolium-based assay to study the production of superoxide radicals by tobacco cell cultures challenged with avirulent zoospores of Phytophthora paracitica var nicotiana. Plant Physiol

The relationship between the production of reactive oxygen spe-cies and the hypersensitive response (HR) of tobacco (Nicotiana tabacum L.) toward an incompatible race of the Oomycete Phyto-phthora parasitica var nicotianae has been investigated. A new assay for superoxide radical (O2 2) production based on reduction of the tetrazolium dye sodium,3*-(1-[phenylamino-carbonyl]-3,4-tetrazolium)-bis(4-methoxy-6-nitro) benzene-sulfonic acid hydrate (XTT) has enabled the quantitative estimation of perhydroxyl/super-oxide radical acid-base pair (HO2 z/O2 2) production during the re-sistant response. Tobacco suspension cells were inoculated with zoospores from compatible or incompatible races of the pathogen. Subsequent HO