Origin of facultative heterochromatin in the endosperm of Gagea lutea (Liliaceae)

Citation
J. Greilhuber et al., Origin of facultative heterochromatin in the endosperm of Gagea lutea (Liliaceae), PROTOPLASMA, 212(3-4), 2000, pp. 217-226
Citations number
40
Categorie Soggetti
Plant Sciences","Cell & Developmental Biology
Journal title
PROTOPLASMA
ISSN journal
0033183X → ACNP
Volume
212
Issue
3-4
Year of publication
2000
Pages
217 - 226
Database
ISI
SICI code
0033-183X(2000)212:3-4<217:OOFHIT>2.0.ZU;2-2
Abstract
Facultative heterochromatin occurs not only in certain animals in connectio n with sex determination but also in members of at least one plant genus, G agea (Liliaceae s. str.), but here in the course of embryo sac development, fertilization, and endosperm formation. The present contribution intends t o provide undebatable photographic and cytometric evidence, previously not available, for the events in the course of which three whole genomes in the pentaploid endosperm nuclei of Gagea lutea become heterochromatinized, In this plant, embryo sac formation usually follows the Fritillaria type, i.e. , the embryo sac is tetrasporic, and a "1 + 3 position" of the spore nuclei is followed by a mitosis in which the three chalazal spindles fuse and two triploid nuclei are formed. A triploid chalazal polar nucleus is derived f rom one of these, which contributes to the pentaploid endosperm. These nucl ei in the chalazal part of the embryo sac show stronger condensation compar ed with the micropylar ones. The pyenosis of the triploid polar nucleus is maintained and even enhanced during endosperm proliferation, while the micr opylar polar nucleus and the sperm nucleus maintain their euchromatic condi tion. The origin of the heterochromatic masses in the endosperm nuclei from the three chalazal genomes of the central cell is unambiguously evident fr om the distribution of heterochromatic chromosomes in the first endosperm m itosis and the following interphase. DNA content measurements confirm a 3 : 2 relationship of heterochromatic and euchromatic chromosome sets, which i s usually maintained up to the cellularized endosperm. Pycnotic nuclei in t he chalazal part of megagametophytes are characteristic of several embryo s ec types, but only for Gagea spp. it is documented that such nuclei can tak e part in fertilization and endosperm formation.