The Rhizoplast (Flagellar Rootlet) of Naegleria

Abstract

<p> The rhizoplast (flagellar rootlet) of the amebaflagellate Naegleria gruberi has been studied in sectioned cells and in the isolated state. Since the organelle arises, as do the other components of the flagellar apparatus, through a de novo assembly, and possibly a de novo synthesis during the ameba-to-flagellate transformation, the characterization of the rhizoplast's nature may be of importance in the study of a differentiation process in a eukaryotic cell. </p> <p> Structurally, the organelle is a periodically-banded, longitudinally fibrous structure arising in the basal body area of the cell and tapering towards its end in the cytoplasm adjacent to the nucleus. The attachment of the organelle to the basal bodies is mediated through the interbasal body connector and the rhizoplast-associated microtubules. Attachment to the nucleus is unlikely as it has never been unequivocally demonstrated in electron-microscope studies. </p> <p> Rhizoplasts exhibit a distinct periodicity composed of alternating electron-opaque and electron-transparent bands. Variations in the width of both bands has been observed and is discussed in terms of the possible role of the organelle as an anchor and stapilizing structure for the flagellar complex, with contractility and elasticity being discussed as possible mechanisms of this variation. </p> <p> An isolation and partial purification of the rhizoplast has been achieved and is described with reference to its possible use as a tool in the biochemical analysis of the rhizoplast. An aggregation phenomenon of dissolved rhizoplast material by divalent cations has been observed and is discussed, keeping in mind the similar phenomena exhibited by the contractile proteins paramyosin and tropomyosino Collagen, which exhibits a reaggregation from solution, is discussed and tentatively discarded as a possibility for rhizoplast material due to its tendency towards solubilization rather than reaggregation in solutions containing divalent cations. </p>