STATUS OF COUMESTROL AND 4',7-DIHYDROXYFLAVONE IN ALFALFA FOLIAGE EXPOSED TO OZONE

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 7 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.