Ecological Role of Cyanogenesis in Plant and Fungal Populations in Natural Ecosystem

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Japanese elder, Sambucus racemosa subsp. Sieboldiana showed the property of cyanogenic polymorphism in relation to the presence or absence of cyanogenic glucosides and -glucosidase. Wild populations of Sambucus were surveyed with reference to cyanogenic and acyanogenic forms from Pacific coast to inner mountain range in Miyagi Prefecture. As altitude increase, there was a corresponding increase in the percentage of cyanogenic form. Reverse is also true of acyanogenic form. The present cline, however, was contrary to that of Trifolium repens widely distributed in Europe and Near East. The field observation and the feeding preference tests in the laboratory did not find selective eating of cyanogenic and acyanogenic Sambucus by caterpillar, Spilosoma inaequalis.As regards cyanogenic fungi, six species of basidiomycetes were newly determined to be cyanogenic. Of these, basidiocarps of Marasmius maximus revealed the toxic actions to seed germination of lettuce as well as microorganisms and small animals in a laboratory assay. In a field assay, the detectable harmful effect was also found in the ambient gas of these fruiting bodies which recorded more than 20 ppm hydrogen cyanide concentration in an artificially closed condition. It seems unlikely that cyanogenesis is a decisive factor for suppressing bacterial populations on the cyanogenic fruiting bodies. In addition, There were no detectable productions of cyanide from profusely developed mycelial layer of any cyanogenic species in the field.