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Assembly and Motility of Eukaryotic Cilia and Flagella. Lessons from Chlamydomonas reinhardtii

2001; Oxford University Press; Volume: 127; Issue: 4 Linguagem: Inglês

10.1104/pp.010807

1532-2548

Carolyn D. Silflow, Paul A. Lefebvre,

Microtubule and mitosis dynamics

Cilia and flagella are among the most ancient cellular organelles, providing motility for primitive eukaryotic cells living in an aqueous environment.During adaptation to life on land, some groups of organisms, including advanced fungi, red algae, cellular slime molds, conifers, and angiosperms, lost the ability to assemble flagella (Raven et al., 1999).The centriole or basal body, which organizes the assembly of flagella, also is absent in these groups.In other lineages, flagella were retained only on gametic cells.Land plants are believed to have arisen from one group of green algae, the charophytes (for review, see Bhattacharya and Medlin, 1998; Qiu and Palmer, 1999), in which the only flagellated cells are motile sperm.The first land plants, bryophytes, which are thought to be the ancestors of higher plants, also produce flagellated sperm cells that require water to swim to the egg.Ultrastructural features of the basal body apparatus in the flagellated cells have provided important morphological data for phylogenetic studies of algae and bryophytes.The absence of centrioles and flagella in all but sperm cells also characterizes seedless vascular plants (pteridophytes) including ferns and the genus Equisetum (Raven et al., 1999).Water is required for these sperm to swim to the archegonium containing the egg.A further adaptation for colonization on land developed in gymnosperm phyla represented by cycads and gingko.These plants produce pollen grains that are transferred to the vicinity of the female gametophyte.A pollen tube extends toward the archegonium and bursts to release flagellated sperm that swim through the released fluid to fertilize the egg.Sperm in seedless vascular plants, cycads, and gingko are large (up to 300 m in diameter), spectacularly complex cells that swim with hundreds to thousands of flagella.The de novo synthesis of the centrioles during the formation and differentiation of