Antenna replacement in the evolutionary origin of chloroplasts

Cyanobacterial phycobilisomes and phycobiliproteins

“…In the reaction carried out by heme oxyge nase, three O 2 molecules are used in a two stage pro cess [6], which makes it possible to make conclusions concerning the evolutionary sequence of emergence of the chlorophyll and phycobilin branches of pigment biosynthesis. Since the latter branch requires oxygen, accumulation of which in the atmosphere occurred only after emergence of chlorophyll bearing oxygenic phototrophs, phycobilins probably developed later than chlorophyll [7].…”

“…As a result of the primary and subsequent endosymbioses, swallowed but undigested cyanobacterial cells became a precursor of all chloroplasts [7,31]. Eukaryotic pho tosynthetics possess the chloroplast pigment apparatus of the same type as cyanobacteria; it consists of a PS I complex, a PS II complex, and an auxiliary antenna.…”

“…However, PBP biosynthesis and PBS mainte nance in the chloroplasts require much more energy compared to these two complexes. Gradual loss of motility and development of the primary and second ary cell wall accompanying colonization of dry land by plants resulted in greatly enhanced requirements for CO 2 assimilation, which became incompatible with the preservation of the PBS antenna with its high energy requirements [7]. Among eukaryotes, PBS sur vived in red algae, since their PBS absorb light in the "green window" of chlorophyll light transmission at great depths; weakly developed cell walls of the red algae are compensated for by calcification of the thal lus.…”

What Happened to the Phycobilisome?

“…Nitrogen is a limiting resource in most environments. Stadnichuck and Tropin [47] have pointed out that the LHC proteins are more economical than the phycobiliproteins in terms of the number of amino acids required to bind a chromophore. Using their figures, this comes out to 4–6 chromophores per 100 amino acids for the average LHC protein in either lineage, compared to only one chromophore per 100 amino acids for the average phycobiliprotein (not counting the non-pigmented linkers).…”