Production of brassinolide-like substances by fungi.

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Brassinolide activity was screened in methanol extracts of the cells of 1098 fungal strains, accordind to rice lamina inclination test. Thirty two strains were found to show as high as 10 ng/g wet cell-level activity. They belong to Cunninghamella, Penicillium, Trichoderma, Aspergillus, Cladosporium and others. Productivity of brassinolide activity was present prejudically among fungal genera, but commonly in the genus. The activity per cells did not depend on the composition of culture media even when various steroidal compounds were added. The activity in methanol extracts was separated mainly into two fractions in silica gel column chromatography; one which was more hydrophobic than brassinolide and the other which was markedly hydrophilic. The former one was the major substance, weighing 60% of the total active fractions. Four and a half g of the hydrophobic substance was purified from 7 kg wet cells of Cunninghamella blakesleeana by successive extraction with methanol, ethyl acetate, and acetone, column chromatographys on almina and silica gel, and preparative HPLC. The substance was identified by TLC and GC/MS as monoolein. Commercial products of monoolein from plants also showed brassinolide activity. Activity of monoolein was one twenty thousandth of brassinolide and was detected at a level of 10 <micro> g/ml. Oleic acid was tenth as active as monoolein. Physiological role of oleic acid and its derivatives in plant was discussed.