SOME ULTRASTRUCTURAL OBSERVATIONS ON THE MODE OF ASSOCIATION OF MICROTUBULES WITH THE PLASMALEMMA IN EPIDERMAL TENDON SELLS OF THE RIVER CRAB

The ultrastructural aspects of the association of microtubules (MTs) w ith the plasmalemma in epidermal tendon cells of the river crab, Potam on dehaani, were studied by thin-section electron microscopy combined with detergent treatment. In the tendon cell, MTs were linked laterall y by anchoring filaments to the plasmalemma via a submembranous electr on-dense layer called the plasmalemmal undercoat. To further clarify h ow such anchoring filaments are spatially related to the plasmalemma t hrough the undercoat, we carefully examined and compared thin-section images obtained from various specimen preparations using saponin and T riton X-100. When the tissues were treated with saponin or Triton, ele ctron-dense materials in the undercoat were extracted in varying degre es to expose internal substructures. The undercoat appeared to show a two-layer organization, the inner and outer layers. In more extracted samples, filamentous networks became prominent in the outer layer. Anc horing filaments were seen to attach to such filamentous networks, whi ch in turn were linked to the plasmalemma proper. Thus, it may be reas onable to consider that the filamentous network constitutes the core s tructure of the plasmalemmal undercoat which is structurally reinforce d by extractable electron-dense materials.