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Heat Shock Protein Synthesis in Propagules of Fusarium oxysporum f. sp. niveum. S. Freeman, Department of Ornamental Horticulture, ARO, The Volcani Center, Bet Dagan 50250, Israel; C. Ginzburg(2), and J. Katan(3). (2)Department of Plant Pathology and Microbiology, The Hebrew University of Jerusalem, Faculty of Agriculture, Rehovot 76100; (3)Department of Ornamental Horticulture, ARO, The Volcani Center, Bet Dagan 50250, Israel. Phytopathology 79:1054-1058. Accepted for publication 17 April 1989. Copyright 1989 The American Phytopathological Society. DOI: 10.1094/Phyto-79-1054.

Germlings of Fusarium oxysporum f. sp. niveum respond to elevated temperatures by synthesizing a set of heat shock proteins (HSPs) with apparent molecular masses of 95, 83, 80, 74, 70, 35, and 18 kD. Vital fluorescent staining in germlings decreases in intensity after exposure to elevated temperature levels. Reduction in percentage of intensely stained germlings at 35 and 36 C corresponds to appearance of HSPs. HSP synthesis is observed in germlings as early as 10 min after exposure to heat stress and declines gradually after transfer of the germlings to 25 C. Thermotolerance to high temperatures of 43 or 44 C is acquired by preheating germlings at sublethal levels. This was determined by measurement of survival upon dilution plating, by vital fluorescent staining and incorporation of l-[35S]methionine into protein. The protection effect is abolished in the presence of cycloheximide, indicating dependence on protein synthesis.

Additional keywords: fluorescein diacetate, weakening.