The surface pattern of Paramecium tetraurelia in interphase: an electron microscopic study of basal body variability, connections with associated ribbons and their epiplasmic environment

Abstract

Summary In Paramecium tetraurelia, thousands of basal bodies with their three associated rootlets are anchored into the submembranous skeleton, the epiplasm, which is itself segmented into cortical units. In this study, we redescribe more precisely (after Pitelka [31], Hufnagel [19] and Allen [1]) the architecture of these structures after detergent treatment and tannic acid contrast reinforcement. Although this technique leads to loss of membranes and of some labile cytoskeletal elements, it allows to better underline how the three rootlets are linked together and to the basal body. The postciliary microtubules and ciliary rootlets (Kd fibers) are bound together by a “fingered node”, and the transverse microtubules to the previous fibers by dense links. The anterior basal body of the pairs is linked to the ciliary rootlet by a newly identified architecture in this species, the “bone-like node” [1]. A specific ciliary domain can be defined in the epiplasm of each cortical unit: epiplasmic rings encircling the basal bodies are closely apposed on the thicker part of the epiplasm and can include some apertures along the basal bodies towards the cilia. The thickness of the epiplasm seems to vary according to the presumptive elongation direction of the cortical units. Each basal body associated rootlet is specifically linked to the epiplasm itself. Because of their unexpected set of linkage organization, these rootlets may ensure the ciliary cohesiveness in the interphase cell as well as the transmission of the ciliary polarity during division as it was previously discussed [19]. We also show for the first time that there is a variability of the basal body architecture at the cellular level: its height, and the number of cartwheel elements change depending on its location on the cortex and its morphogenetical history; the longest basal bodies with 5 cartwheel elements are found in territories which result from hyperduplication and become invariant, i.e. do not undergo duplication during the next divisions, as is the case along the sutures and in the left oral and cortical areas [22]. These results are discussed in terms of morphogenetical behavior.