FACTORS RESPONSIBLE FOR INHIBITING THE MOTILITY OF ZOOSPORES OF THE PHYTOPATHOGENIC FUNGUS APHANOMYCES COCHLIOIDES ISOLATED FROM THE NONHOST PLANT PORTULACA-OLERACEA

In a survey of plant secondary metabolites regulating the behaviour of Aphanomyces cochlioides zoospores, me found that root extracts of Por tulaca oleracea inhibited zoospore motility, Bioassay-directed fractio nation of Portulaca constituents revealed that the inhibitory activity was dependent on the interaction of two chemically different factors. These were identified as a phenolic compound, N-trans-feruloyltyramin e, which by itself was active as a zoospore stimulant, and an acidic c ompound, 1-linoleoyl-2-lysophosphatidic acid monomethyl ester, which h ad zoospore-repellent activity. When Chromosorb W AW particles coated with a mixture of these pure compounds were bioassayed in Petri dishes , the inhibitory effect on zoospore motility was identical with that c aused by root tip or root extracts of P. oleracea. Inhibited zoospores rapidly settled to the bottom of the Petri dishes where they initiall y encysted, and then germinated within 1-2 h, This is the first report of factors which inhibit zoospore motility without killing or burstin g the zoospores. (C) 1998 Federation of European Biochemical Societies .