Inhibition of photosynthetic pigments in cucumber cotyledons as a principle for a bioassay with fluridone

The response of etiolated cucumber (Cucumis sativus L. cv. National Pickling) cotyledons to fluridone was investigated in terms of inhibition of photosynthetic pigments, and utility as a bioassay. At a light intensity of 35 W/m², chlorophyll levels were higher in the controls, than at either 12.9 W/m², or 75 W/m². Fluridone inhibition was also more pronounced at that intensity. Significant differences between treatments were established as early as 24 h after exposure to light, when at the lowest fluridone concentration of 0.001 μg/ml, chlorophylls and carotenoids were inhibited 25 and 35% respectively. The system's simplicity and sensitivity suggest its use as a bioassay. It is shown that simple monochromatic absorbances of acetone extracts can satisfactorily estimate chlorophylls and carotenoids. Concentrations of fluridone as minute as 10^?9 moles/ litre are easily delected, and the system could feasibly detect even lower levels.