The intracellular origin of flagellar hairs in the chrysophyceae and xanthophyceae

ABSTRACT Cells of the chrysophycean flagellate Olisthodiscus luteus contain bundles of aligned tubes and fibres within membrane-limited vesicles. Each element in a vesicle consists of a tapering portion 0 · 25 μm long, a shaft 1 · 5 μm long and a terminal fibre 0·25μm long; the shaft is approximately 15 nm in diameter and has a helical cross-banding with a periodicity of 8 nm. The flagellar hairs of Olisthodiscus have identical morphology and dimensions to these internal elements. Zoospores of the filamentous xanthophycean algae Bumilleria sicula, Heterococcus spp. and Tribonema spp. have similar internal vesicles containing aligned tubes and fibres with precisely the same morphology and dimensions as the flagellar hairs: base plus shaft, 1· 2 μm long, two terminal fibres per hair, 0 · 5—0 · 8 μm long, shaft diameter of approximately 15 nm and a helical periodicity of the shaft of 8 nm. The aligned tubes are absent from the vegetative xanthophycean cell, appear during zoosporogenesis and disappear during early stages of zoospore settlement. It is suggested that the aligned tubes and fibres are potential flagellar hairs which are formed in the perinuclear space (and possibly other regions of the endoplasmic reticulum) and are then transported to the cell surface in vesicles of the ER for deposition on the flagella. A review of information available on the Chrysophyceae, Xanthophyceae, Phaeophyceae and Bacillario phyceae indicates that internal formation of flagellar hairs is probably the rule in the heterokont algal groups, and a similar process apparently occurs in at least the dinoflagellates, the crypto-monads and some aquatic fungi among other groups of organisms with hairy flagella.