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Ultrastructural Changes in Corn Leaves after Inoculation with Helminthosporium maydis, Race T. J. A. White, Research Electron Microscopist, Department of Plant Pathology, University of Missouri, Columbia 65201; O. H. Calvert(2), and M. F. Brown(3). (2)(3)Associate Professor, and Assistant Professor, respectively, Department of Plant Pathology, University of Missouri, Columbia 65201. Phytopathology 63:296-300. Accepted for publication 4 September 1972. DOI: 10.1094/Phyto-63-296.

Corn seedlings, of a strain having Texas male-sterile cytoplasm, were inoculated with conidia of Helminthosporium maydis, race T. Infected leaf tissues were sampled at 6, 12, 24, and 48 hr after inoculation. Electron microscopic examination of these tissues revealed that the first detectable change, rupture of the tonoplast, occurred within 6 hr. By 12 hr, chloroplasts had become spherical, and numerous vacuolelike bodies were present in the plastid stroma. At 24 hr, the plasma membrane had ruptured, chloroplast envelopes had become disorganized, and the mitochondrial matrix appeared to be absent. In many cells, the plastid envelopes had disintegrated, and numerous irregular, osmiophilic bodies were interspersed within the lamellar systems. By 48 hr, the chloroplast lamellae had clumped together and had undergone extensive structural breakdown. Tissue samples taken from 48-hr necrotic lesions revealed the most advanced stages of cell breakdown.

Additional keywords: negative-image membranes.