Wyniki wyszukiwania - Biblioteka Nauki

1

Controversy around apomixis

100%

Czapik R.

Acta Biologica Cracoviensia. Series Botanica

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2000

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tom 42

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nr 2

EN

Three problems are discussed in the present article: the currently changing meaning and range of the term "apomixis," opinions on the normality of apomictic processes, and the relation between vegetative and apomictic reproduction. The differences in opinion on these matters reflect the authors’ subjective views, which cannot be avoided in dealing with complex phenomena that are difficult to manipulate experimentally. However, the increase in the number of synonyms that can be observed in the current literature is not useful in discussions and does not make statements easier to interpret. Thus, special attention should be paid to the precise use of terminology in discussions and articles on apomixis and related processes.

2

Individual variability of endosperm in apomictic Chondrilla juncea L.

100%

Pajak M.

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nr 1

3

Genetics of gametophytic apomixis - a historical sketch

75%

Nogler G. A.

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1994

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tom 08

4

Controversy around apomixis

75%

Czapik R.

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nr 1

5

Frequency of apomixis in seed plants of Poland

75%

Czapik R. , Koscinska-Pajak M.

Folia Morphologica

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1998

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tom 57

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nr 1

6

Epigenetic aspects of sexual and asexual seed development

75%

Rodrigues J. C. M. , Koltunow A. M. G.

Acta Biologica Cracoviensia. Series Botanica

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2005

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tom 47

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nr 1

EN

In angiosperms, seed development initiates after a double fertilization event in the female gametophyte, in which one male sperm cell fuses to the central cell to form the endosperm and the other to the egg cell to form the embryo. Sexually-derived seed is thus characterized by maternal and paternal contributions to the progeny. Some plant species have the capacity to form seeds asexually, a process known as apomixis. This mode of reproduction is characterized by a bypass of meiotic reduction and the absence of paternal contribution to the embryo, resulting in a seed with an embryo genetically identical to the mother. Little is known about the molecular events that regulate apomictic development. Recent findings show that the apomictic and sexual developmental programs share molecular components, suggesting that apomixis is a deregulated sexual program. Furthermore, the identification of apomictic developmental features in fertilization-independent seed (fis) mutants in the sexual model plant Arabidopsis has also shed light on the molecular events that control sexual seed development, and has opened new questions as to the molecular nature of autonomous seed development. FIS-class genes are homologues of the Polycomb Group (PcG) chromatin remodelling factors conserved in Drosophila and humans, where they have been implicated in gene repression and control of cell fate throughout development. fis phenotypes are affected by DNA methylation, a DNA alteration associated with heterochromatin formation and gene silencing. Thus, the chromatin environment can be manipulated to make certain regions of the genome more or less susceptible to transcription; this form of control, in which gene expression patterns are altered without a change in the DNA sequence itself, is defined as epigenetic regulation. Different aspects of plant development have been shown to be controlled by epigenetic regulation. This review will highlight recent advances in understanding the epigenetic control of seed development. They are discussed in light of a model whereby altered epigenetic mechanisms might lead to complete maternal control of reproductive development as seen in apomixis.

7

Frequency of apogamety

75%

Solntseva M. P.

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nr 1

8

An efficient screen for embryological events using ripe seeds of monocots and dicots

63%

Matzk F. , Meister A.

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nr 1

9

The genetic and molecular analysis of apomixis in the model plant Hieracium

63%

Koltunow A. M.

Acta Biologica Cracoviensia. Series Botanica

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2000

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tom 42

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nr 2

EN

The dicotyledonous genus Hieracium contains apomictic and sexual species, and is used as a model to study apomixis at the molecular level. Apomixis is facultative and occurs by apospory followed by autonomous embryo and endosperm formation. The sexual pathway initiates first, then apomixis begins with the differentiation of initial cells, and in the more successful apomicts the apomictic pathway displaces the sexual. Genetic analysis showed that apomictic seed set is dependent on the activity of a dominant locus and also modifiers that can influence the fate of initial cell development. The initiation of apomixis is presaged by the altered expression of a DEFICIENS homologue. Initiation of apomixis is not related to alterations in callose deposition or ß-l,3-glucanase activity as has been proposed in other apomicts. Ablation of ovule tissues showed that the funiculus or substances flowing through it exert a negative effect on aposporous initial cell formation. Initial cells were capable of forming embryo sacs, embryos and endosperm in the altered context of ovule development resulting from funicular cell ablation. Signals from surrounding ovule tissues might therefore play a role in directing initial cell fate and the progression of apomixis. We propose that the apomixis locus confers the potential for the components of apospory and autonomous embryo and endosperm development, while other genes that normally regulate ovule and seed maturation may act as modifiers. The combination of locus and modifier activity results in a particular mode of apomixis. The locus and the modifiers require characterization to effectively manipulate apomixis in crops where this beneficial trait is largely absent.

10

Professor Romana Czapik - biographical note

63%

Jankun A.

Acta Biologica Cracoviensia. Series Botanica

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1999

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tom 41

11

Apomixis in cultivated strains of Poa pratensis L.s.l.

63%

Jankun A. , Kaszuba J.

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nr 1

12

Embryo and endosperm relations at early stages of their development in lchemilla subsect. Heliodrosium [Rosaceae]

63%

Izmailow R.

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1994

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tom 08

13

Alterations in ovule development and the influence on apomixis in Hieracium

63%

Koltunow A. M. , Johnson S. D.

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nr 1

14

Timing of megasporogenesis in Tripsacum species [Poaceae] as related to the control of pomixis and sexuality

63%

Leblanc O. , Savidan Y.

|

1994

|

tom 08

15

Intraindividual variability of endosperm in autonomously apomictic Chondrilla juncea L.

63%

Koscinska-Pajak M.

Acta Biologica Cracoviensia. Series Botanica

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1998

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tom 40

EN

The data concerning endosperm type in Chondrilla juncea L. from Europe, Asia and Australia have been the subject of controversy. This study investigated the problem embryologically in an individual plant growing on an experimental field. Two endosperm types, nuclear and cellular, were observed to be present in inflorescences of the same plant. Both types of endosperm were formed after open pollination as well as after emasculation; however, cellular endosperm predominated slightly after open pollination. The development of endosperm preceded embryo development independently of endosperm type. Intraspecific variability of endosperm type in the investigated plant seems to be genetically conditioned, and it may be modified by external conditions.

16

Apomixis in ferns. Alternation of generations without syngamy and meiosis

63%

Zenkteler E.

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nr 1

17

Embryology of apomixis in diploid sugar beet

63%

Seilova L. , Sedlovskiy A. , Tyupina L.

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nr 1

18

Further observations in embryo sac development in Alchemilla L. [subsection Heliodrosium Rothm.]

63%

Izmailow R.

|

tom 36

EN

Origin of embryo sacs was examined in further two Alchemilla species: A. acutiloba and A. montícola. The central region of multicellular archesporium shows meiotic tendencies but as a rule, the meiotic division did not advance further than up to I ptophase. Apomeiotic embryo sacs arise from unreduced cells, either from megaspore mother cells (diplospory) or from cells of somatic character (apospory). In the same ovule a few embryo sacs of both types may be formed. Usually only one of them reaches a distinct prevalence and the full maturity.

19

Theoretical aspects of apogamety in angiosperms

63%

Czapik R.

Bulletin of the Polish Academy of Sciences. Biological Sciences

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1997

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tom 45

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nr 2-4

20

How to detect apomixis in Angiospermae

63%

Czapik R.

|

1994

|

tom 08