(redirected from nucellar)
Also found in: Dictionary, Thesaurus, Medical.


The oval central mass of tissue in the ovule; contains the embryo sac.



the central part, or nucleus, of the ovule in seed plants; it is homologous to the megasporangium of ferns (Pteridophyta). Inside the nucellus, the megaspore mother cell is differentiated. The nucleus of the megaspore mother cell divides, forming four nuclei, from which subsequently arise four megaspores. Three of the megaspores atrophy, and one develops into the female gametophyte (in gymnosperms, the primary endosperm; in angiosperms, the embryo sac). In some flowering plants the tetranuclear cell divides into two binuclear cells or does not divide at all; the gametophyte originates from one binuclear cell (the second one atrophies) or from the entire tetranuclear cell. The nucellus preserved in the seed is called the perisperm.

References in periodicals archive ?
acid phosphatase, was detected in the pollination drop of Welwitschia, it is not known whether it was secreted into the drop by nucellar tissue, or it arrived in the drop after degenerative formation of the pollen chamber.
Although there were accessions with similar names (for example, Nucellar Satsuma and Satsuma Owari), they do not appear to be related to each other.
After growing through nucellar tissue for three days, from one to several pollen tubes approach the micropylar end of the female gametophyte [ILLUSTRATION FOR FIGURE 4A OMITTED].
The embryo was prominent and the nucellar tissue was no longer present in control kernels indicating normal progression toward completion of the endosperm cell division stage.
In addition to the sexual or zygotic embryo, most citrus seeds also present nucellar embryos, formed by somatic nucellus cells, characterizing the nucellar polyembryony (FROST; SOOST, 1968).
The taxonomy and phylogeny of Citrus are complicated due to the high rate of bud mutation and the sexual compatibility between Citrus and related genera and the asexual reproduction through nucellar embryony, which is characteristic in several Citrus species and most rootstock (Frost, 1943; Cameron, 1979).
developing MTOC is associated with the membranes of the nucellar beak,
asexual reproduction by seeds) is a common trait in the genus, being apospory (in which a non reduced megagametophyte originates from a somatic cell, usually a nucellar cell) the most frequent type, and diplospory (in which a non reduced megaspore originates from the reproductive cell itself, with the later failing to successfully complete meiosis) only of occasional occurrence (Quarin, 1992).
Relationships of seed size and shape with polyembryony and the zygotic or nucellar origin of Citrus spp.
Citrus isozymes: Genetics and distinguishing nucellar from zygotic seedlings.
in a cross-section of the nucellar zone of one seed, a pollen tube was
Nucellar callus of `Femminello' lemon selected for tolerance to Phoma tracheiphila toxin, shows enhanced release of chitinase and glucanase into the culture medium.