text: The enzyme is important for carotenoid biosynthesis during chloroplast biogenesis. In developing plastids, its activity prevents the over-reduction of the plastoquinone pool. Knockout plants for PTOX exhibit phenotypes of variegated leaves with white patches. Without the enzyme, the carotenoid synthesis pathway slows down due to the lack of oxidized plastoquinone with which to oxidize phytoene,  a carotenoid intermediate.  The colorless compound phytoene accumulates in the leaves, resulting in white patches of cells. PTOX is also thought to determine the redox poise of the developing photosynthetic apparatus and without it, plants fail to assemble organized internal membrane structures in chloroplasts when exposed to high light during early development.