Observations On The Micro-and Ultrastructure Of The Cortical Pigment Granule And Mucocyst In Diaxonella Pseudorubra

On the taxonomic studies of Hypotrich ciliates, the cortical Pigment Granule, which related to cell color, has attracted the attention of the researchers. And the distributions and shapes of these granules are always regarded as the morphological taxonomy evidence. At present, some researches about cortical pigment granule in Trichototaxis songi have been done. But a problem is why the pigment granule could inherit permanently, and the distribution, heredity and function in the cellular activities have not been discussed deeply. So in this dissertation, the cortical pigment granules and the cytoplasmic mucocyst of Hypotrichous ciliate Diaxonella pseudorubra were investigated by using differential interference contrast microscopy and TEM. And two kinds of pigment granules in the cortex and mucocysts in the cytoplasm have been observed.1 pigment granules(1) differential interference contrast microscopy showed that the cell present red or faint red colors, and there are two kinds of granules in the cortex, including red granules and colorless granules. A majority of pigment granules arrange in linear and incompact rows between RMC and MVC, MVC and LMC, 2 rows of LMC; in the dorsal cortex, the pigment granules distribute irregularly, and the distribution model of granules and dorsal kineties have no obvious correlation. High power lens showed that the pigment granules are spheroidal, which can be divided into two kinds with different size: diameter of the bigger one is 0.5μm, the smaller is 0.2μm. in addition, several granules arranged closely and formed moniliform, this probably is the graph which formed by the binary fission.( 2 ) TEM showed that the cortical granules present low electronic density and spheroidal, most of them get together or arrange in string beads in compact cytoplasm. And also the binary fission were observed, one of the manner is that a high electronic density diaphragm present in the big granule center, and separate the granule into two parts; another is that the big granule divided continuously, and produce many small granules.The results indicate that the two kinds of cortical pigment granule of Diaxonella pseudorubra might have common origin and bear relations with the heredity of ciliate color, the different size were form by different division models. And the further studies about the functions will still be needed.2 Mucocyst(1) Structure and distributionMucocysts look like an oval structure surrounded with a smooth membranous layer and containing crystal-like substances internally. In occurrence of mucocysts, some vesicles present in deep compact cytoplasm. These vesicles were surrounded by low density materials, and then become the mucocysts precursors. With the electronic density of substances increase, the precursors blossom into mature mucocysts. The distribution of the crystal-like substance changes and gradually the crystal-like substance forms three recognizable parts: head, body and tail. The matured mucocysts can move towards pellicle by means of "amebism" with their head ahead and fuse its head part plasma membrane with the pellicle. The fusion may result in an opening of mucocyst on the pellicle. Then the inclusion of mucocyst is extruded out of the organelle and finally the remaining empty mucocyst becomes part of the pellicle and can no longer be observed.(2) Characteristics different from the mucocysts found in other ciliatesIn Diaxonella pseudorubra cytoplasm, some mucocysts extrusomes present in deep compact cytoplasm. In addition, the mature mucocysts in Diaxonella pseudorubra can be divided into three parts: head, body and tail, while these morphological characteristics are similar to Urostyla grandis, but different to Tetrahymena. The mature mucocyst seemed to be undulated before extrusion. The mucocyst moved to pellicle by means of "amebism" and there the inclusion of mucocyst was extruded out. This progress is beried similarity to those observed in Urostyla grandis. In addition, the SEM showed that there are some spheroidal granular protuberances or hollows in the surface, while this phenomenon is also observed in Urostyla grandis. They must be the traces of the extrusion which have not been repaired immediately. The separate distribution of the developing mococysts of Diaxonella pseudorubra is obviously different from those ciliates such as Tetrahymena whose mucocysts are found to be located constantly in the pellicle region between ciliate lines and two alveoluses.(3) FunctionsThe appearance of some holes after mucocyst extruded suggests that mucocysts might take an important part in the physical activity in the Diaxonella pseudorubra. The extrusion process of mucocyst and the fusion of the membranous structure of mucocyst with the pellicle after extrusion indicate that mucocysts in Diaxonella pseudorubra could have some contribution to the pellicle renewal and material flow of the ciliate, and also promote the metabolism.3 conclusionsThe present study provides abundant morphological data for the investigation into extrusomes in protozoan ciliates. To sum up, the findings in this research are of significant scientific importance for the further elucidation of the specificity of cytoarchitectures and the relationship between the cytoarchitectures and their functions, the deep of the knowledge about the occurrence of organelles, the changes of cortical structure and the mechanisms of cell regulation in cellular activity of ciliates.