Algal Plastids: Their Fine Structure and Properties

Abstract

The origin of plastids was by endosymbiosis of a cyanobacterium or an ancestor of cyanobacteria but the exact origin is still an area of contention. The three groups of primary plastid bearing algae (chlorophytes, rhodophytes and glaucocystophytes) arose at about the same time. The other algae arose by secondary endosymbiosis of a plastid-containing primary host by a second host (euglenophytes, cryptophytes, chloroarachniophytes, chromophytes and apicomplexans). The origin of Chl b is at the prokaryotic stage. However, the route from a prochlorophyte chlorophyll a/b binding (pcb) protein to an algal/higher plant CAB/ CAC protein is not clear evolutionarily. The origin of Chl c1 + Chl c2 is probably from MgDVP, which occurs in prochlorophyte cyanobacteria, but there is no clear evidence on how it, and its association with characteristic xanthophylls, arose. Thylakoid membrane appression arose along with CAB/CAC proteins but true grana arose somewhere near the base of streptophytes, which are the forebears of land plants (embryophytes).