title: On the origin of mitosing cells. 1967
abstract: A theory of the origin of eukaryotic cells ("higher" cells which divide by classical mitosis) is presented. By hypothesis, three fundamental organelles: the mitochondria, the photosynthetic plastids and the (9+2) [9(2)+2] basal bodies [kinetosomes] of flagella [undulipodia] were themselves once free-living (prokaryotic) cells. The evolution of photosynthesis under the anaerobic [anoxic] conditions of the early atmosphere to form anaerobic bacteria, photosynthetic bacteria and eventually blue-green algae (and protoplastids) is described. The subsequent evolution of aerobic metabolism in prokayotes to form aerobic bacteria (protoflagella [undulipodia] and protomitochondria) presumably occurred during the transition to the oxidizing atmosphere. Classical mitosis evolved in protozoan-type cells millions of years after the evolution of photosynthesis. A plausible scheme for the origin of classical mitosis in primitive amoeboflagellates [amoebomastigotes] is presented. During the course of the evolution of mitosis, photosynthetic plastids (themselves derived from prokaryotes) were symbolically acquired by some of these protozoans to form the ["eukaryotic" deleted] algae and the green plants.  The cytological, biochemical and paleontological evidence for this theory is presented, along with suggestions for further possible experimental verification. The implications of this scheme for the systematics of the lower [smaller] organisms is discussed.
authors.affiliation: Department of Biology, Boston University, Massachusetts, USA.
authors.forename: L
authors.initials: L
authors.lastname: Sagan
mesh_terms: D000818:Animals; D005075:Biological Evolution; D002468:Cell Physiological Phenomena; D000458:Cyanobacteria; D056890:Eukaryota; D005057:Eukaryotic Cells / Q000166:cytology / Q000502:physiology* / Q000648:ultrastructure*; D005111:Extrachromosomal Inheritance / Q000235:genetics / Q000502:physiology; D005407:Flagella; D049673:History, 20th Century; D008928:Mitochondria; D008938:Mitosis; D010084:Oxidation-Reduction; D010788:Photosynthesis; D018087:Plastids; D011387:Prokaryotic Cells / Q000166:cytology / Q000502:physiology / Q000648:ultrastructure; D013559:Symbiosis