Mature Hair Cells Research Articles

Ultrastructure of the hairs of the filamentous green alga Bulbochaete hiloensis (Nordst.) Tiffany: an apoplastidic plant cell with a well developed Golgi apparatus

Bulbochaete hiloensis is a filamentous green alga in the Oedogoniales. It possesses colourless hair cells, the ultrastructure and development of which are unusual in several respects: (1) The initial wall of the hair cell is formed by eversion of a pre-formed pad of cell wall material (Cook, 1962). (2) The hair cells are apoplastidic, even lacking colourless remnants of plastid material. (3) A nucleolus is lacking from young and mature hair cell nuclei, though it is not known whether one is present in the earliest stages. (4) Despite the absence of chloroplasts, starch reserves, and a nucleolus, the ultrastructure of the cytoplasm is characteristic of intensive granulocrine secretory activity. Massed cisternae of rough endoplasmic reticulum and numerous dictyosomes, together with associated transitional and secretory vesicles, are present. Substrate for the biosyntheses in these systems must enter the hairs via plasmodesmata, which exist in the basal wall. The product is probably a mucilage, exported to the exterior through a system of pores which pierce the outer wall of the hair. (5) Microtubules lie in the hair, and in its bulbous base, where some may be interpreted as having a role in anchoring the nucleus. (6) The significance of the apoplastidic and anucleolate condition is discussed.

Cochlear development. Some electron microscopic observations of maturation of hair cells, spiral ganglion and Reissner's membrane.

The hair cells differentiate before their nerve endings make synaptic contact in the organ of Corti. Each hair cell develops stereocilia and a cuticle prior to innervation. The ectodermal endolymphatic layer of Reissner's membrane has some features in common with fluid transport epithelia. Each spiral ganglion Schwann cell initially envelops many nerve fibers, but eventually myelinates only a single fiber.