Observations on the Substructure of Flagellar Fibres

Abstract

The substructure of the outer and central fibres of the flagella of Trichonympha and other flagellates has been examined by electron microscopy, using negatively-stained material. Periodicities revealed in the micrographs have been analysed by studying the optical diffraction patterns obtained from them. Outer and central fibres appear to be essentially similar in substructure and are made up of a number of longitudinal filaments which form the wall of the hollow fibres. The filaments are 40-50 Å apart, centre to centre, and are beaded, the beads (or subunits) giving rise to an axial repeat along the filaments of 40 Å and a basic surface lattice of 40 x 50 Å. In collapsed or disintegrating fibres no other substructural features are usually visible. In intact fibres, however, additional longitudinal periodicities are apparent. An 80-Å spacing is prominent, and there is commonly also a strong 160-Å repeat. These appear to be orders of a fundamental 480-Å period. The long spacings are thought to arise as departures in the arrangement of the subunits from the simple 40 x 50 Å lattice, the perturbations probably occurring both radially and in the plane of the surface of the fibre. In the central fibres additional material is present, spaced at 160 Å and probably corresponding to the central sheath previously described from sectioned material. Observations on the arms of the outer fibres are described.