Studies On Cortical Ciliatures And Extrusomes Of The Hypotrichous Ciliate Oxytricha Granulifera (Ciliophora: Hypotrichida)

Ciliates are the most advanced groups of protist, because of its complex cortex system. Cortical ciliatures and extrusomes are the important structures of cortex system which have always been the hotspot of the ciliate research field. The research of cortical ciliatures and extrusomes of hypotrichous not only provides important theoretical basis for the systematics and taxonomy but also have great significance to indicate the formation of organelle structure and the regulation of exocytosis in eukaryocyte. The cortex system of hypotrichous ciliate Oxytricha granulifera not only has developed ciliatures that hypotrichous ciliate generally possessed, but also has extrusomes. Therefore, O. granulifera is a good experimental material for the studies on cortical ciliatures and extrusomes of hypotrichous ciliate. In this paper, the author studied the cortical ciliatures and extrusomes of O. granulifera collected from the Kingdom of Saudi Arabia (hereinafter referred to as Saudi), by the following methods: differential interference contrast microscopy, protargol impregnation, scanning electron microscopy, transmission electron microscopy, alcian blue staining, and staining with methyl green-pyronin. The main results and conclusions are as follows.1 The morphology and morphogenesis of cortical ciliatures of O. granuliferaIn the Saudi population of O. granulifera, there are altogether 21-23 frontal-ventral-transverse cirri:8 frontal cirri; 8-10 ventral cirri; 5 transverse cirri. The ventral cirri are composed of 2 pretransverse ventral cirri and 6-8 postoral ventral cirri. Invariably 5 dorsal kineties; the first three dorsal kineties are throughout the cell; fourth dorsal kinety starts at the slightly behind of mid-body and terminates at the posterior end; fifth dorsal kinety begins with the anterior end of the cell and ends at the 1/3 of cell length. By contrast, we found that the number of postoral ventral cirri of the Saudi population of O. granulifera is distinctly increased compared with the Austrian population and Xi’an population of O. granulifera (Three postoral ventral cirri), and the number of dorsal kineties of the Saudi population of O. granulifera is consistent with the Austrian population, but disagree with the Xi’an population (Six dorsal kineties). Therefore, there are intraspecific variation in the number of postoral ventral cirri and dorsal kineties among the three populations of O. granulifera.It can be traced back to the morphogenetic process that the intraspecific variation of the number of postoral ventral cirri. The result that the morphogenesis of cortical ciliatures in the Saudi population of O. granulifera shows that the fifth frontal-ventral-transverse cirral (FVT) anlage is divided into 7-9 cirri, and the postoral ventral cirri derive from the fourth and fifth FVT anlagen in the proter and opisthe. Thus, it can be seen that the reason that the increase of the number of the postoral ventral cirri is that the fifth FVT anlagen is divided into more cirri. The Saudi population corresponds well to the Austrian population in the morphogenesis of dorsal kineties. The dorsal kineties anlagen 1-3 develop separately within the parental dorsal kineties 1-3; then the third dorsal kinety anlage fractures and migrates at the posterior end, which becomes the fourth dorsal kinety anlage; the fifth dorsal kinety anlage develops independently at the front of the lateral of right marginal row. In conclusion, the author speculated that the intraspecific variation of the number of cirri maybe exist widely in the different populations of oxytrichid ciliates.2 The structure and function of the extrusomes of O. granuliferaUltrastructural observation showed that the colourless cortical granules are a special type of extrusomes in O. granulifera. Mature extrusomes are elongated ellipse, which bounded by a single membrane and the electron density gradually reduces form exterior to inner, and it is almost no electron density at the cavity on the anterior. The anterior end of the mature extrusomes is close to the pellicle, and distributed in longitudinal, diagonal or arc rows. Compared with other types of extrusomes, the morphology and localization of extrusomes in O. granulifera are different with the extrusomes in lower groups of ciliate, but similar to the extrusomes in the hypotrichous ciliate Architricha indica. Therefore, we can speculate that the extrusomes may be the same type in O. granulifera and A. indica.During the process of the development of extrusomes, firstly, the fibrous substances with low electron density are appeared at the edge of the vesicles, then fibrous substances constantly assemble to form a high electron density fibrage and migrate to the center of the vesicles, finally, the vesicles become the mature extrusomes which the posterior part is filled with the different electron dense fibrous substances and the anterior part has hollow cavity. During ejection, the anterior membrane of extrusomes fuses with the plasma membrane and the extruded contents often remain in the surface of the cells after extrusion, which similar to the extrusomes of A. indica. The extrusomes of O. granulifera can be stained by alcian blue 8GS which can rapidly stain mucin, carboxyl and sulphate-containing mucosubstances, therefore, the extrusomes of O. granulifera may contain some mucosubstances. Under the stimulus of methyl green-pyronin, the extrusomes of O. granulifera are numerously discharged, and the extruded contents of extrusomes get together to form a "capsule" which packes the ciliate in it, thus, it might be a defensive response to harmful conditions.