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The actin and the tubulin cytoskeleton organization during the differentiation of the embryo-suspensor in Alisma plantago-aquatica was studied in comparison with the development of embryo, using immunofluorescence detection and rhodamine-phalloidin assay. At the early stage of the suspensor basal cell development (from 2- to ~10-celled embryos) microfilaments form an abundant network in the cytoplasm of the basal cell, while the microtubules form a delicate network. At the mature stage of development (from a dozen to several dozen-celled embryos), in the suspensor basal cell, the microfilaments and microtubules were localized from micropylar to chalazal pole of the cell. At the micropylar end of the basal cell a high amount of actin and tubulin material was observed. The microfilaments were mainly arranged parallel whereas numerous bundles of microtubules distributed longitudinally or transversally to the long axis of the cell. At this stage of basal cell functioning, some bundles of microtubules appeared to pass close to the nucleus surface. Microtubules were also observed distributed at the chalazal pole of the basal cell. At the senescence stage of the suspensor basal cell (>100-celled embryos) the actin and tubulin filaments disorganize, some disrupted microfilaments and microtubules were observed in the cytoplasm of the basal cell. At all stages of the suspensor basal cell development in the embryo cells an extensive actin and tubulin network was observed.
The actin cytoskeleton of endosperm and of the mature endosperm chalazal haustorium cell of Rhinanthus serotinus was examined by immunohistochemistry and epifluorescence microscopy. A prominent actin cytoskeleton composed of numerous cross-linked filaments is present at the distal pole of the chalazal haustorium cell. Thick, longitudinally oriented bundles of microfilaments localize in transvacuolar cytoplasmic strands. A meshwork of delicate actin filaments surrounds the large polytene nuclei; some of the filaments radiate from the nuclear envelopes. Abundant and clearly visible actin filaments also occur at the proximal pole of the haustorium cell. A network of microfilaments in cortical cytoplasm and F-actin arrays associated with nuclei are found in endosperm proper cells.
We examined the development of the endosperm chalazal haustorium of Rhinanthus serotinus, using histochemical assays and light and electron microscopy. The chalazal haustorium is a huge single cell containing two enlarged nuclei. The nuclei are located in the middle of the haustorium cell. At the chalazal end of the haustorium cell structure, ultrastructural study revealed the presence of a transfer wall forming wall ingrowths. At all examined stages of haustorium cell development we identified insoluble polysaccharides, proteins, nucleic acids and lipid droplets. Macromolecules were especially abundant in the fully differentiated haustorium cell. Our results suggest that the endosperm chalazal haustorium is a site of intense metabolic activity.
Karyological processes of differentiation of the suspensor of Gagea lutea (L.) Ker Gawl. were compared with the development of the embryo proper. The zygote divides into the smaller apical cell and the bigger basal cell, which becomes the basal cell of the suspensor. The mature suspensor consists of a huge basal cell and a few chalazal cells. The nuclear DNA content of the suspensor basal cell attains a high degree of ploidy, up to 128C. Nuclei with the highest ploidy level of 128C were found only in fully differentiated basal cells of more than 20-celled embryos. During polyploidization, the volume of the nuclei increased, and changes in the chromatin structure of polyploid nuclei were noted. With increasing levels of ploidy, polytene chromosomes were observed in the suspensor nucleus. Changes in DNA content, nucleus size and chromatin structure point to endoreduplication as the mechanism of polyploidization of the suspensor in Gagea lutea.
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