Wyniki wyszukiwania - Biblioteka Nauki

1

Molekularny mechanizm endoreduplikacji u roślin wyższych

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Rewers M.

Kosmos

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2017

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tom 66

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nr 3

475-485

PL

Proces endoreduplikacji stanowi alternatywną formę cyklu komórkowego, podczas której następuje amplifikacja jądrowego DNA, po której nie zachodzi jednak mitoza i podział komórki. Mechanizm molekularny tego procesu w dużej mierze opiera się na białkach uczestniczących w typowym cyklu komórkowym i polega na zablokowaniu mitozy wraz z ponownym zainicjowaniem replikacji DNA. W endoreduplikacji ważną rolę odgrywają kinazy zależne od cyklin oraz ich białka regulatorowe - cykliny. Podczas tego procesu aktywność tych białek jest regulowana na poziomie transkrypcyjnym i potranslacyjnym. Zmiana aktywności kinaz zależnych od cyklin może wynikać ze zmniejszenia dostępności cyklin w wyniku zablokowania ich transkrypcji oraz ze zmian statusu fosforylacji kinaz zależnych od cyklin. Może być również negatywnie regulowana poprzez fosforylację podjednostki kinazy zależnej od cyklin przez kinazę WEE1 oraz poprzez interakcję z inhibitorami kinaz zależnych od cyklin. Regulacja na poziomie potranslacyjnym polega natomiast na ukierunkowanej destrukcji cyklin przez kompleks promujący anafazę/cyklosom. Szczegółowe omówienie mechanizmów molekularnych tego procesu zostało przedstawione w poniższym artykule.

EN

Endoreduplication represents an alternative form of the cell cycle in which nuclear DNA amplification occurs, but it is not followed by mitosis and cell division. The molecular mechanism of this process is largely based on proteins involved in typical cell cycle and involves block of mitosis and re-initiation of DNA replication. Cyclin-dependent kinases and theirs regulatory proteins - cyclins are the key components of endoreduplication. During the process, activity of these proteins is regulated at the transcriptional and post-translational levels. Changes in the activity of cyclin dependent kinases may be due to a reduced availability of cyclins resulting from blocking of respective genes transcription and to changes in the status of cyclin-dependent phosphorylation of kinases. It can be also negatively regulated by phosphorylation of the cyclin-dependent kinase subunit by kinase WEE1, and by interaction with inhibitors of cyclin dependent kinases. Post-translational regulation occurs via targeted destruction of cyclins by the anaphase promoting complex/cyclosome. A detailed discussion of the molecular mechanism of these processes is presented in this article.

2

Comparative cytogenetic analysis of diploid and hexaploid Chenopodium album Agg.

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Kolano B. , Siwinska D. , Maluszynska J.

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nr 4

293-298

EN

Two cytotypes of Chenopodium album, diploid (2n=2x=18) and hexaploid (2n=6x=54), were analysed using flow cytometry and a FISH experiment. The genome size was indicated as 1.795 pg for the diploid and 3.845 pg for the hexaploid plants which suggested genome downsizing in the evolution of hexaploid cytotype. Double FISH with 25S rDNA and 5S rDNA allowed three to five homologue chromosome pairs to be distinguished depending on the cytotype. The Variation in size and number of rDNA sites between the polyploid C. album and its putative diploid ancestor indicated that rDNA loci underwent rearrangements after polyploidization. Flow cytometry measurements of the relative nuclear DNA content in the somatic tissue of C. album revealed extensive endopolyploidization resulting in tissues comprising a mixture of cells with a different DNA content (from 2C to 32C) in varying proportions. The pattern of endopolyploidy was characteristic for the developmental stage of the plant and for the individual organ. Polysomaty was not observed in the embryo tissues however endopolyploidization had taken place in most tested organs of seedlings. The endopolyploidy in diploid and hexaploid C. album was compared to find any relationship between the pattern of polysomaty and polyploidy level in this species. This revealed that polyploid plants showed a decline in the number of endocycles as well as in the frequency of endopolyploidy cells compared to diploid plants.

3

Salinity has no effect on polysomatic pattern in seedlings of Trifolium pratense and T. repens

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Acta Biologica Cracoviensia. Series Botanica

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2017

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tom 59

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nr 1

EN

Endopolyploidy is a condition of a cell containing reduplicated genetic material in its nucleus. Cells with the nuclei of different ploidy levels are often present within a single polysomatic organism. Endoreduplication is thus a modified cell cycle that omits cytokinesis and leads to chromatin replication in the endopolyploid cells. This study aimed to research the effect of salinity on endopolyploidy of Trifolium pratense and T. repens. Both species are important pasture legumes and belong to the genus Fabaceae with the well documented endopolyploidy occurence. Endopolyploidy levels in the seedlings treated with 0, 30, 60, 90 and 120 mM NaCl were investigated by flow cytometry. The seedling organs were evaluated during three ontogeny stages. The cytometric data plotted on a histogram showed the presence of 2C-16C nuclei in T. pratense and 2C-8C in T. repens. The hypothesis that salinity induces additional endocycles was not confirmed. Our results show that the distribution of nuclei among ploidy levels does not differ markedly between the treatment groups and the control ones. Additionally, only minor changes were observed among the endoreduplication indexes (EI) of plant organs after exposure to various salt concentrations. Endopolyploidy patterns within the salt-treated seedlings during ontogeny are similar to the controls. We suggest that endopolyploidy in Trifolium species is a conserved genetic trait, rather than an adaptation to salinity stress. The analyses of the roots of T. pratense at stage III show that with the increased concentrations of NaCl the length of roots decreased, but no evident changes in endopolyploidy occured.

4

Endopolyploidy patterns during development of Chenopodium quinoa

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Kolano B. , Siwinska D. , Maluszynska J.

Acta Biologica Cracoviensia. Series Botanica

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2009

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tom 51

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nr 2

85-92

EN

Patterns of endopolyploidy were studied in embryos and seedlings during early development. Relative nuclear DNA content was measured with DAPI staining and flow cytometry. Somatic tissue of Chenopodium quinoa (Chenopodiaceae) revealed extensive endopolyploidization; tissues comprised mixtures of cells with DNA content ranging from 2C to 16C in varying proportions. Endopolyploidy patterns corresponded to the developmental stage and the individual organ. Polysomaty was already present in the radicle of the embryo in the imbibited seed. During seedling development, endopolyploidization took place in many examined organs (roots, hypocotyls, cotyledons) to different extents. The C-value was highest in the differentiated root, where up to 50% of the cell underwent one or two endocycles. Endopolyploidization was not present in nuclei from leaves and the shoot apex