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The Quantitative Relation Between Plant and Bacterial Cells Involved in the Hypersensitive Reaction. John G. Turner, Department of Plant Pathology, University of Missouri, Columbia 65201; Anton Novacky, Department of Plant Pathology, University of Missouri, Columbia 65201. Phytopathology 64:885-890. Accepted for publication 24 January 1974. DOI: 10.1094/Phyto-64-885.

Dead plant cells, selectively stained with Evans blue, were detected in symptomless tobacco leaves inoculated with the incompatible pathogen, Pseudomonas pisi, at concns lower than those required to give a confluent hypersensitive reaction (HR). With each concn of P. pisi, plant cell death was first detected within 1-2 h, and rose to a max 6 h, after inoculation. No further plant cell death occurred after this interval. A 1:1 ratio was observed between the number of cells of P. pisi introduced and the number of dead plant cells present 6 h or more after inoculation. In all cases, dead plant cells occurred singly and were randomly distributed throughout the tissue. Confluent HR occurred when the ratio of bacteria to total plant cells was 1:4 or lower. In tissues inoculated with Pseudomonas tabaci, the compatible pathogen, cell death was detected only 18 h after inoculation, and it increased as the typical disease syndrome developed. No cell death was detected in tissues inoculated with the saprophyte, Pseudomonas fluorescens. We concluded that HR will occur at the cell level, invisible to the unaided eye, in tissues naturally inoculated with small numbers of incompatible bacteria.