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Incompatibility Conditioned by the Mla Gene in Powdery Mildew of Barley: The Halt in Cytoplasmic Streaming. W. R. Bushnell, Research plant physiologist, Cereal Rust Laboratory, U.S. Department of Agriculture, ARS, and Department of Plant Pathology, University of Minnesota, St. Paul 55108; Phytopathology 71:1062-1066. Accepted for publication 29 January 1981. Copyright 1981 The American Phytopathological Society. DOI: 10.1094/Phyto-71-1062.

Cytoplasmic streaming stopped in host epidermal cells of barley under attack by Erysiphe graminis f. sp. hordei when host-parasite incompatibility was conditioned by the Mla gene. The cytoplasm halted 13 hr before the host cells collapsed hypersensitively. These events in tissues partially isolated from coleoptiles were viewed at 1- to 4-hr intervals by direct observation, or continuously by time-lapse cinephotomicrography. The hypersensitive collapse of cells usually occurred 1826 hr after inoculation when the primary haustorium was partly formed. The halt in cytoplasmic streaming that preceded this collapse was, in turn, preceded by a 0.5-hr period in which host cytoplasm accumulated in small amounts near the haustorium. Organelles within this cytoplasm moved in a localized, restricted fashion. The results indicate that an early metabolic or structural change associated with gene-for-gene incompatibility interferes with cytoplasmic movement.