Sperm ultrastructure in the diatoms Melosira and Thalassiosira and the significance of the 9 + 0 configuration


The most complete account to date of the ultrastructure of flagellate cells in diatoms is given for the sperm of Thalassiosira lacustris and Melosira moniliformis var. octogona, based on serial sections. The sperm are uniflagellate, with no trace of a second basal body, and possess a 9 + 0 axoneme. The significance of the 9 + 0 configuration is discussed: lack of the central pair microtubules and radial spokes does not compromise the mastigoneme-bearing flagellum’s capacity to perform planar beats and thrust reversal and may perhaps be related to sensory/secretory function of the sperm flagellum during plasmogamy. The basal bodies of diatoms are confirmed to contain doublets rather than triplets, which may correlate with the absence of some centriolar proteins found in most cells producing active flagella. Whereas Melosira possesses a normal cartwheel structure in the long basal body, no such structure is present in Thalassiosira, which instead possesses ‘intercalary fibres’ linking the basal body doublets. No transitional helices or transitional plates are present in either species studied. Cones of microtubules are associated with the basal body and partially enclose the nucleus in M. moniliformis and T. lacustris. They do not appear to be true microtubular roots and may arise through transformation of the meiosis II spindle. A close association between cone microtubules and tubules containing mastigonemes may indicate a function in intracellular mastigoneme transport. No correlation can yet be detected between methods of spermatogenesis and phylogeny in diatoms, contrary to previous suggestions.

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We thank Dr. I. Inouye (Tsukuba University) for his helpful suggestions about sectioning and TEM observation. We also thank to Dr. K. Hasegawa and Dr. K. Ogane for the contribution to digitisation of films.

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Correspondence to Masahiko Idei.

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Handling Editor: Adrienne R. Hardham

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Supplementary Fig. 1

Selected serial transverse sections from the flagellum to the basal body in Melosira moniliformis var. octogona. TEM. ae Enlargements of Fig. 8b, c, e, k and n, respectively. Scale bar = 200 nm (in a) (PSD 1791 kb)


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Idei, M., Osada, K., Sato, S. et al. Sperm ultrastructure in the diatoms Melosira and Thalassiosira and the significance of the 9 + 0 configuration. Protoplasma 250, 833–850 (2013).

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  • 9 + 0 configuration
  • Basal bodies
  • Diatoms
  • Flagellar ultrastructure
  • Mastigonemes
  • Sperm