EFFECT OF TAXOL AND RELATED-COMPOUNDS ON GROWTH OF PLANT-PATHOGENIC FUNGI

Taxol, currently in use as therapy for refractory ovarian cancer, has no known function in the plant(Taxus brevifolia) from which it is isol ated. In an effort to explore its biological role, we investigated the effect of Taxol and related compounds on the growth of plant pathogen ic fungal hyphae. Taxol and cephalomannine inhibited the growth of sev eral fungi, especially Phytophthora and Pythium species (Oomycetes) an d Rhizoctonia solani (Basidiomycetes). Baccatin III had no effect on t he growth of any fungus tested. Strains of Aspergillus (Deuteromycetes ) and Fusarium (Ascomycetes) were not inhibited by any taxane. As litt le as 1.0 nmol of Taxol or cephalomannine severely retarded radial gro wth of Phytophthora species on solid medium. A dose-dependent effect w as also evident in liquid culture assays down to 0.1 mu M Taxol, with total inhibition of mycelial growth at 1.0 mu M. At lower concentratio ns of Taxol, the fungal mycelium reached stationary stage 4 days later than the controls, indicating growth retardation rather than death. W hen hyphae were transferred to Taxol-free media, growth resumed as nor mal. Active doses are roughly 600 times lower than an estimated concen tration of Taxol in Toxus needles. It is proposed that Taxol may be a preformed antifungal defense compound in Taxus species.