Temperature-induced modifications in size and pattern of microtubular organelles in a ciliate, Dileptus

Supernumerary microtubules were found in the so-called sensory cilia, in addition to a sensory axoneme. The supernumerary microtubules were not structurally connected to a basal body, but were probably anchored to clusters of dense material inside the ciliary shaft. The frequency of appearance of the supernumerary microtubules was found to be temperature-dependent: the higher the temperature during formation of sensory cilia, the greater was the number of supernumerary microtubules in cross-sections, and the more cross-sections contained them. The possibility is discussed that the formation of the supernumerary microtubules is not due to formation of new nucleating sites inside the cilium. Instead, the microtubules may be remnants of a previously existing axoneme, separated from the basal body during the formation of a sensory cilium. Some of the microtubules of the released axoneme may persist as the supernumerary microtubules, if capped with dense material or some other structure within the ciliary shaft.