The beta,epsilon-carotenoid, lutein, is specifically required for the formation of the oligomeric forms of the light harvesting complex in the green alga, Scenedesmus obliquus

The secondary developmental mutants, 2A'-34, 2A'-67, 1 and 2A'-67,3b of Scenedesmus obliquus exhibit specific deletions in the biosynthetic pathway of the beta,epsilon- and beta,beta-carotenoids. The inability to convert zeaxanthin to the beta,beta-epoxycarotenoids (antheraxanthin, violaxanthin and neoxanthin) in the 2A'-67 strains does not influence the photosynthetic competence or alter the types of pigment-protein complexes formed upon illumination of dark grown cultures. However, the absence of the beta,epsilon carotenoids, lutein and loroxanthin, in 2A'-34 and 2A'-67,3b limits the synthesis of chlorophyll b and the light-harvesting complex (LHC-II). This inhibition is clearly correlated with the inability of these mutants to develop the oligomeric forms of the LHC-II. The carotenoid composition of the monomeric form of the light harvesting chlorophyll protein, LHCP(3), when purified from each of the mutant types, showed wide variations. No absolute requirement for the beta,beta-epoxycarotenoids in the formation of the LHCP(3) was noted, whereas its further oligomerization to the dimer and trimer forms, LHCP(2) and LHCP(1), specifically require the beta,epsilon-carotenoids. It is noteworthy that the majority of algae that synthesize a chlorophyll b containing LHC also develop a beta,epsilon-carotenoid as the principle carotenoid of that pigment-protein complex.