The Inhibition of Carotenoid Biosynthesis in Green Algae by SANDOZ H 6706: Accumulation of Phytoene and Phytofluene in Chlorella fusca

Prolonged cultivation of the green alga Chlorella fusca under heterotrophic conditions and in the presence of sub-lethal concentrations of SAN H 6706 (4-chloro-5-(dimethylamino)-2-(α,α,α-tri-fluoro-m-tolyl)-3 (2H)-pyridazinone) leads to an accumulation of phytoene and phytofluene. The content of chlorophylls and coloured carotenoids of the cells treated with this herbicide, compared with normal untreated cells, is diminished by about 90% and 95% respectively, but the total amount of carotenoids, including colourless phytoene and phytofluene, is increased by 65%. This suggests that SAN H 6706 causes increased accumulation of carotenoids by eliminating a biosynthetic control mechanism, so that the endproducts of the biosynthetic chain no longer control the rate of precursor formation.