β-carotene is the intermediate exported from the chloroplast during accumulation of secondary carotenoids in Haematococcus pluvialis
Grünewald K., Hagen C.
Recent findings on the localization in Haematococcus pluvialis of an early and a late enzyme in astaxanthin synthesis have suggested the sequential involvement of two compartments, the chloroplast (site of early synthesis) and the cytoplasmic lipid vesicles. Here the intermediate transported across the chloroplast envelope into the cytoplasm is elucidated by means of the inhibitors diphenylamine (DPA) and 2-(4-chlorophenylthio)-triethylamine (CPTA). Based on the amounts of the intermediates accumulated upon inhibitor treatment and their occurrence in the lipid vesicle fractions, it is concluded that the transport takes place after β-ionone ring cyclization. A non-vesicle mechanism of β-ionone carotenoid transport from the chloroplast towards the cytoplasmic lipid vesicles via carotenoid binding proteins is suggested.