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Status of Coumestrol and 4,7-Dihydroxyflavone in Alfalfa Foliage Exposed to Ozone. B. Hurwitz, Former graduate research assistant, Department of Plant Pathology, The Pennsylvania State University, University Park 16802, Present address of senior author: Department of Plant Pathology, New York State Agricultural Experiment Station, Cornell University, Geneva, NY 14456; E. J. Pell(2), and R. T. Sherwood(3). (2)Associate professor, Department of Plant Pathology, The Pennsylvania State University, University Park 16802; (3)Adjunct professor, plant pathologist, SEA-FR, U.S. Department of Agriculture, U.S. Regional Pasture Research Laboratory, University Park. Phytopathology 69:810-813. Accepted for publication 14 February 1979. Copyright 1979 The American Phytopathological Society. DOI: 10.1094/Phyto-69-810.

Alfalfa plants, 7 wk old, were exposed to 387 μg/m3 (0.20 ppm) ozone for 2.5 hr, and the most severely injured leaves were harvested 48 hr after exposure. In a second experiment, 8.5-wk-old plants were exposed to 580 μg/m3 (0.30 ppm) ozone for 2 hr and middle-aged leaves were harvested 0 and 24 hr after exposure. Coumestrol was never detected in ozonized leaves or nonozonized controls from either experiment. At least seven fluorescent compounds accumulated in alfalfa foliage in response to ozone exposure. One of the compounds was identified as 4,7-dihydroxyflavone. As symptom severity increased, the concentration of 4,7-dihydroxyflavone in the foliage increased. Foliage exhibited more ozone-induced injury and accumulated higher levels of 4,7-dihydroxyflavone in trials conducted during December, January, and February than in trials conducted in August.