Coumarin concentrations that inhibited growth of Pythium sp. rapidly decreased the rate of incorporation of [14C]glucose into the mycelium. Coumarin also reduced drastically the carbohydrate and protein content of the cytoplasm and, to a lesser extent, the amino acid content and cell wall fraction. Enzymes related to the metabolism of cell wall polysaccharides were not affected during early exposure to the inhibitor. The possible mechanism of coumarin action via inhibition of glucose uptake is

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... iscussed in the light of the present findings. Coumarin (1,2-benzopyrone) is known to affect growth in higher plants (2, 9, 11, 12, 20, 25) as well as growth and spore germination of certain fungi (8, 16, 17, 27) . It was recently reported that coumarin specifically inhibits the incorporation of ['4C]glucose into "cellulose" of mung bean plumular tissue without any detectable effect on the absorption of glucose by this organ (10).'Since coumarin is known to inhibit the growth of oomycetes more strongly than it does that of other fungi (8) and since the cell walls of oomycetes are known to contain cellulose (1, 5, 22, 23) , it interested us to determine if coumarin would have the same metabolic effect in a Pythium species as that revealed for higher plants (10, 13). MATERIALS AND METHODS Organism and culture conditions. Pythium sp. (ATCC 24619) was maintained and grown in Seymour MSPS agar medium (24). Actively growing cultures were transferred from 9-cm petri dishes to 250-ml Erlenmeyer flasks containing 50 ml of liquid medium consisting of Seymour MSPS without agar supplemented with the desired additions of ['4C]glucose and coumarin. ['4C]glucose and coumarin were sterilized separately by filtration (Seitz no. 5115-C3 disks) and mixed with cooled medium. All media were prepared to give the same final concentration after addition of the inhibitor and labeled glucose. Inocula were obtained as agar plugs cut out with a 5-mm sterilized cork borer and were transferred to the desired medium for incubation at 22°C in the dark without agitation. Growth curve determination. At 48-h intervals, liquid-grown cultures were harvested by centrifugation at 500 x g for 20 min and washed twice by centrifugation in cold distilled water. The washed mycelia were lyophilized, and the dry weight of the initial inoculum (mean of 10 disks) was subtracted to obtain a growth value. These determinations were made in triplicate. t Permanent address: