ScienceWeek: "Schimper in 1885 (2) suggested that chloroplasts were derived from symbiotic microorganisms, and Mereschkowsky in 1905 argued more extensively for the development of different
types of chloroplasts from different types of cyanobacteria (3,4). Much later, the role of bacteria in symbiogenesis was championed by Margulis (5). Many scientists have provided the crucial data that convincingly show the close relationship between chloroplasts and cyanobacteria, including similar
ribosomes, RNA polymerases, and other cellular machinery (briefly reviewed in ref.1). Current research suggests that the cyanobacterial/eukaryote symbiosis occurred only once but diverged rapidly to three major lineages: the greens, the reds, and the rather odd lineage called glaucocystophytes. The greens
are the green algal/land-plant group. The reds are the red algae, now producing much of the agarose consumed by molecular biology labs.

References (abridged):
1. Martin, W. , Rujan, T. , Richly, E. , Hansen, A. ,Cornelsen, S. , Lins, T. , Leister, D. , Stoebe, B. , Hasegawa,M. & Penny, D. (2002) Proc. Natl. Acad. Sci. USA 99, 12246-12251.
2. Schimper, A. F. W. (1885) Jahrbüecher füer WissenschaftlicheBotanik 16, 1-247.
3. Mereschkowsky, C. (1905) Biol. Zent. Bl. 25, 593-604.
4. Martin, W. & Kowallik, K. V. (1999) Eur. J. Phycol. 34,287-295.
5. Margulis, L. (1981) Symbiosis in Cell Evolution: Life andIts Environment on the Early Earth (Freeman, San Francisco)."

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