Inhibition of astaxanthin synthesis in the green alga,Haematococcus pluvialis

The effect of a range of inhibitors on the carotenoid biosynthetic pathway of the microalga Haematococcus pluvialis has been studied during normal growth and during the induction of astaxanthin synthesis. Diflufenican and norflurazon had similar effects and resulted in the almost complete inhibition of secondary carotenoid synthesis together with a build up of the acyclic carotenoid precursor, phytoene. In contrast, the inhibitor CPTA blocked cyclisation of lycopene and was seen to act differentially on the β- and ∊-cyclases. Both diphenylamine and 1-aminobenzotriazole had the effect of blocking the synthesis of astaxanthin and the other secondary carotenoids by preventing the introduction of oxygen functions. As a direct result treated cells accumulated large levels of β-carotene instead. Selective use of inhibitors of carotenogenesis demonstrated that the accumulated lycopene and β-carotene could act as a precursor for astaxanthin synthesis.