KARYOTYPING OF AMOEBA PROTEUS.

In this paper, the protocol which we have developed to get satisfactory spreads of Amoeba proteus mitotic chromosomes is presented, and the process of karyotyping this amoeba species is described. This protocol allows obtaining of extended chromosomic with repeatable chromomeres pattern in individual chromosomes. We have shown that metaphase in «B¼-strain amoebae (one of the type strains of A. proteus in the Amoebae Strains Collection at the Institute of Cytology) contains 27 chromosome pairs with homologous chromomeric pattern. It is ascertained that chromomeric pattern is chromosome-specific feature. The bank of images of DAPI- and YoYo1-banded individual metaphase chromosomes of «B¼-strain of A. proteus is presented.

MECHANICAL IMPACT ON THE CELL COVERING FINE STRUCTURE OF DINOFLAGELLATES PROROCENTRUM MINIMUM.

Complex cell coverings (amphiesma) of potentially toxic dinoflagellates Prorocentrum minimum include plasma membrane and flattened amphiesmal vesicles with thecal cellulose plates. Two largest thecal plates surround the major portion of dinoflagellate cell as shell valves. We have revealed that P. minimum cells appear to be extremely sensitive to the physical stress: even low speed centrifugation (1200 and 2000 g) leads to a dropping of old coverings shedding (ecdysis) and the formation of viable spheroplasts. Spheroplasts are surrounded only by the plasma membrane beneath which the new amphiesma is formed. These spheroplasts can be a convenient model system for investigation of numerous aspects of cell and molecular biology of the dinoflagellates.

[Light- and electron-microscopic study of pelobiont Pelomyxa secunda (Gruber, 1884) comb. nov. (Archamoebae, Pelobiontida)].

Morphology of a pelobiont Pelomyxa secunda (Gruber, 1884) comb. nov. was investigated at light- and electron-microscopical levels. Locomotive forms are elongated or cigar-shaped. The size of active forms varies from 200 to 300 µm. Larger individuals (up to 400 µm) are not able to directed movement. Organism can produce short, usually finger-shaped hyaline pseudopodia at the frontal side or laterally. The cell coat is represented by amorphous glycocalix, up to 300 nm in thickness. A thin periphery cytoplasmic zone is deprived of any organelles, vacuoles, endocytobionts and other inclusions and separated from main cytoplasm by a layer of arranged microfilaments. P. secunda is multinucleate organism; nuclei are of granular type. The nucleolar material is represented by two forms of discrete structures differing in size and electron density. Two or three layers of short microtubules organized in the parallel arrangement are associated with outer side of the nuclear envelop. P. secunda possess two types of obligate prokaryotic endocytobionts lying in individual symbiontophoric vacuoles. Undulipodia, kinetosomes and root microtubular derivatives are not observed in P. secunda cells as well as any developed cytoplasmic microtubular cytoskeleton.

[CHROMATIN ORGANIZATION IN CELL CYCLE OF AMOEBA PROTEUS ACCORDING TO OPTICAL TOMOGRAPHY DATA].

For the first time the nuclear cycle of large freshwater amoeba Amoeba proteus was studied by the method of optical tomography. The nuclei were fixed in situ in the cells of synchronized culture, stained by DAPI and examined by confocal laser scanning microscope. 3D-images of intranuclear chromatin were studied in details at different stages of nuclear cycle. The obtained data, together with literary ones allow represent the dynamics of structural organization of the nucleus in Amoeba proteus cell cycle in a new fashion. It was concluded that in this species the two-stage interphase takes place, as well as mitosis of peculiar type which does not correspond to any known type of mitosis according to classification existing now. It is presumed that in the course of nuclear cycle the chromosomes and/or their fragments are amplified, this presumption being in a good correspondence with the data about nuclear DNA hyperreplication in the cell cycle of A. proteus. As a result of chromosomes amplification their number may vary at different stages of cell cycle, and it allows to explain the contradictory data concerning the exact number of chromosomes in this species. The elimination of extra-DNA occurs mainly at the stage between prophase and prometaphase. We presume the majority of chromosomes, or may be even all of them to be referred to cholocentric type according to their behaviour during the mitosis.

[Reisolation and redescription of pelobiont Pelomyxa paradoxa Penard, 1902 (Archamoebae, Pelobiontida)].

Morphology of a pelobiont Pelomyxa paradoxa Penard, 1902 was investigated at light- and electron-microscopical levels. Locomoting cells are cigar-shaped. The cells produce many hyaline pseudopodia of digital and conical form at lateral sides of the body. The organism has a pronounced hyaline bulbous uroid with broad peripheral zone of hyaloplasm and many conical hyaline villi. There is a thin layer of amorphous glycocalix at the cell surface. "Structure" and food vacuoles of different size are very abundant in the endoplasm. Two different species of prokaryote endocytobionts are peculiar for P. paradoxa. Uninucleate stage dominates in the life cycle of P. paradoxa. Usually there are no more than 10-12 nuclei in multinucleate forms of P. paradoxa. Pelomyxae nuclei are closely surrounded by thick multilaminar layer and additionally by one more layer, which is formed by small vesicles with electron-dense content. Several irregular-shaped nucleoli are situated at the nucleus periphery. Inside the nucleoli, and sometimes directly in nucleoplasm the small round bodies are revealed, these bodies being formed by tightly packed electron-dense fibrils. Many non-motile flagellae are located mainly in the uroidal zone of the cell. Pronounced lateral root and 50-60 radial microtubules originate from the electrone-dense muft around the kinetosome. All elements of the rootlet system of flagella are limited by peripheral layers of cytoplasm. P. paradoxa occupy an intermediate position between two groups of species of Pelomyxa genus--P. gruberi + P. prima and P. palustris + P. stagnalis + P. belewski, which differ greatly by the organization of their flagella basal apparatus.