Pigment Biosynthesis: Chlorophylls, Heme, and Carotenoids

Comparison of Chlorophyll and Carotenoid Concentrations Among Russian Wheat Aphid (Homoptera: Aphididae)-Infested Wheat Isolines

“…carotenoid pigments may result in the degradation of the membranes (Timko 1998). This may help explain similarities in the patterns of carotenoid and chlorophyll loss in the susceptible and resistant wheat.…”

yellow-in-the-dark Mutants of Chlamydomonas Lack the CHLL Subunit of Light-Independent Protochlorophyllide Reductase

“…Previous studies have shown that the products of three chloroplast genes (designated chlL , chlN , and chlB ) and at least seven nuclear loci (designated y-1 to y-10) are required for light-independent PChlide reduction in the green alga Chlamydomonas reinhardtii (Sager, 1955;Timko, 1998). Cells with mutations in any of the three plastid genes or containing any one of the nuclear y mutations have identical phenotypes, referred to as yellow-in-the-dark , reflecting a loss of chlorophyll formation and the accumulation of the biosynthetic precursor PChlide.…”

“…One mechanism, which is catalyzed by the enzyme NADPH:PChlide oxidoreductase (POR), depends completely on light for its activity (Reinbothe and Reinbothe, 1996;Timko, 1998). Light-dependent POR activity is present in cyanobacteria, green algae, and most nonvascular and vascular plants, and it is the only mechanism used for chlorophyll formation in angiosperms.…”

“…Organisms containing this PChlide reduction mechanism are all capable of chlorophyll formation in the dark. Although a large amount of information is now available on the regulation of POR biosynthesis and activity, little is known about the enzyme that mediates light-independent PChlide reduction (designated LIPOR), the factors that regulate its formation, and the enzyme's requirements for catalytic function.Previous studies have shown that the products of three chloroplast genes (designated chlL , chlN , and chlB ) and at least seven nuclear loci (designated y-1 to y-10) are required for light-independent PChlide reduction in the green alga Chlamydomonas reinhardtii (Sager, 1955;Timko, 1998). Cells with mutations in any of the three plastid genes or containing any one of the nuclear y mutations have identical phenotypes, referred to as yellow-in-the-dark , reflecting a loss of chlorophyll formation and the accumulation of the biosynthetic precursor PChlide.…”

“…Cells with mutations in any of the three plastid genes or containing any one of the nuclear y mutations have identical phenotypes, referred to as yellow-in-the-dark , reflecting a loss of chlorophyll formation and the accumulation of the biosynthetic precursor PChlide. When grown in the light, however, these same cells synthesize chlorophyll and achieve a wild-type phenotype, a result of the presence of a functional light-dependent POR.Although direct biochemical evidence is lacking, the products of the plastid chlL , chlN , and chlB genes are thought to constitute the subunits of an oligomeric complex that catalyzes light-independent PChlide reduction (Bauer et al, 1993;Fujita, 1996;Timko, 1998). The roles of the various y gene products in the process of light-independent PChlide reduction and their possible interactions with chl gene products are not known.…”