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Hemolysins in Potato Plants and Their Relation to Virus Infection. Kang- chien Liu, Former Graduate Assistant, Department of Plant Pathology, The Pennsylvania State University, University Park 16802; John S. Boyle, Professor, Department of Plant Pathology, The Pennsylvania State University, University Park 16802. Phytopathology 64:714-718. Accepted for publication 8 December 1973. DOI: 10.1094/Phyto-64-714.

It was found that foliage extracts from both healthy potato plants and plants infected with viruses hemolyzed red blood cells from various animal sources. The intrinsic substances present in the extracts and responsible for hemolysis were investigated for possible effect on virus infectivity and pathogenesis. Extracts from potato plants chronically infected with tobacco mosaic virus (TMV) yellow strain (Y) alone or TMV-U1 strain (U1) plus potato virus X (PVX) lost most of their hemolytic activity, whereas those plants infected with TMV-U1 or PVX alone retained the activity. Extracts from young leaves of plants infected with TMV-U1, or PVX were distinctly higher in hemolytic activity than those from older leaves, and an inverse correlation between numbers of lesions on indicator plants and hemolytic activity of these extracts was observed. This is not the case with extracts from potato plants chronically infected with TMV-Y or TMV-U1 plus PVX. When extracts of leaves from different positions on a plant infected with PVX were heated at 55 C for 10 min, PVX infectivity increased in all. The increase was greatest in extracts from the lower part of a plant, which also showed the lowest hemolytic activity. Electron micrographs showed similar numbers of PVX particles in extracts from either younger or older leaves. Hemolytic activity was not affected by heat. It is evident that a virus inhibitor is present in potato plants, and that this inhibitor also possesses hemolytic activity. Since heat reduced the effects of inhibitor on virus infection, but not the hemolytic activity, it is conjectured that the activity of the inhibitor might be related to its direct attachment to virus particles rather than any capability for causing a host-directed inhibition of infection.