Ultrastructure and cytochemistry of the Golgi apparatus and related organelles of the secretory ameloblasts of the rat incisor.

Glutaraldehyde-fixed rat incisors were either post-fixed in ferrocyanide-reduced osmium impregnated with the Ur-Pb-Cu technique or incubated in the medium for acid-phosphatase (AcPase) reaction. The Golgi apparatus of the secretory ameloblast was composed of 4-7 cisternae, small vesicles and condensing vacuoles. It formed an elongated, continuous membrane system over from one- to two-thirds of the supranuclear cytoplasm. Condensing vacuoles seemed to be produced from the dilated margins of both Golgi cisternae and GERL. AcPase activity was demonstrated in the inner 2 or 3 Golgi cisternae, in GERL and in some condensing vacuoles and secretory granules within the Tomes process. It thus seemed that primary lysosomes originate from both the Golgi apparatus and GERL. Whereas many lysosomal bodies appeared in the supranuclear cytoplasm, autophagic vacuoles were rare. A well-developed Golgi apparatus and GERL were, therefore, considered to be involved in the digestion of exogeneous materials as well as in the formation of the precursor of enamel matrix. The simple Golgi apparatus consisting of only compactly stacked cisternae and small vesicles, were sometimes observed in the supranuclear cytoplasm and having no clear relationship with rough-surfaced endoplasmic reticula or GERL, may serve as a source of the plasma membranes necessary for continuous renewal of the cisternae of the well-developed Golgi apparatus.