ABSTRACTThe herbicide Sandoz 6706 (metflurazon) inhibits carotene biosynthesis and allows photobleaching of chlorophyll in light-grown green plants. To explore its effects in non-photosynthetic organisms, the influence of metflurazon on pigmentation of nine soil-inhabiting fungi, representing a broad taxonomic spectrum, was investigated. Metflurazon treatment reduced observable intensity of pigmentation in many of these fungi. In the yeastRhodotorula glutinis, herbicide treatment decreasedβ-carotene concentrations and increased the levels of phytoene, a colorless precursor ofβ-carotene. These results suggest that, in this yeast, metflurazon either inhibits a phytoene dehydrogenase or prevents end-product inhibition of phytoene production. Thus, one mechanism of action of the herbicide inR. glutinisis similar to that proposed for some photosynthetic organisms.