Subsidiary components of the flagella of Chlamydomonas reinhardii

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Abstract
Some subsidiary components of flagella from the alga Chlamydomonas reinhardii have been studied in the electron microscope using frayed and partially dispersed material, negatively stained. In all, 5 distinct subsidiary structures have been observed, 3 of which are associated with the 9 pairs of outer tubules and 2 with the central pair of tubules. 1. Radial spokes, about 33 nm long and 5 nm in diameter, are attached at right angles to the A tubule of each outer pair and extend into the lumen of the flagellum in the direction of the central pair of tubules, but do not reach them. The spokes usually occur in pairs along the length of each A tubule. The interval between pairs is about 70 nm and that between the 2 members of each pair about 30 nm. 2. ‘Secondary fibres’. The distal end of each spoke terminates in a hammerhead-like attachment some 10-20 nm by 5 nm with its axis parallel to the long axis of the flagellum. These hammerhead attachments are now identified with the so-called ‘secondary fibres’ previously deduced from micrographs of embedded and sectioned material. There is no evidence from the present work of a continuous secondary fibre throughout the length of the flagellum. 3. Side arms are found attached to the A tubule of each outer pair. These arms, which occur in pairs, are roughly at right angles to the radial spokes which are also attached to the A tubules. The side arm material is distributed along the tubule at regular intervals of about 14 nm. 4. The chemically more stable centre tubule has 2 longitudinal rows of projections, each projection being about 18 nm long with a repeat distance of about 16 nm. 5. Occasionally, on the chemically less stable centre tubule, there is observed one row of projections which are somewhat similar to those on the other tubule. New information has made it possible to reinterpret earlier work and to present a 3-dimensional picture of the external flagellum and its parts.