Accumulation of Colorless Carotenes and Derivatives during Interaction of Bleaching Herbicides with Phytoene Desaturation

Colorless carotenoids were accumulated, analyzed and quantified in heterotrophically- grown Scenedesmus cultures treated with the bleaching herbicide norflurazon. By optical, IR and mass spectroscopy 15-cis as well as all-trans phytofluene, 15-cis phytoenes and traces of its all-trans isomer were identified. Furthermore, a phytoene epoxyde and several hydroxyphy- toenes were assigned. Comparing the concentrations of these phytoene derivatives in hetero-trophic cultures grown in darkness with those in light-grown autotrophic cells, an exchange of phytoene derivatives was observed. Levels of phytoene were much higher in the dark whereas concentrations of hydroxyphytoenes dominated in the light. Other herbicides like fluridone, diflufenican, and difunon accumulate the same colorless carotenoids including phytoene epoxyde and various hydroxyphytoenes. For all herbicides an almost constant hydroxyphytoene to phytoene epoxyde ratio was observed indicating an interrelated formation of both oxygenated phytoene derivatives which can be influenced by light conditions of the cultures.