Nucellus


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nucellus

[‚nü′sel·əs]
(botany)
The oval central mass of tissue in the ovule; contains the embryo sac.

Nucellus

 

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 ?
A single archesporial cell differentiated under a single layer of epidermal cells in the young nucellus (Fig.
Other models have been proposed that depend on the degree of active secretion that is occurring from the nucellus (Tomlinson et al.
com, or MSN Live Search, find more information by searching for these words or phrases: after riping, dioecious, generative cell, integument, microsporangia, microspore mother cell, nucellus, ovule, polyembryony, seed coat, self-incompatible, and tube cell.
As it was observed in the presented study, the nucellus of the Fabaceae ovules is crassinucellate (Prakash, 1987), and which has been considered to be the primitive condition in angiosperms (Sporne, 1969).
Carpel with receptive stigma: in the few conifers with extended siphonogamy the site of pollen reception is imprecise and the target for the pollen tube is still the nucellus or its extension, whereas in Angiosperms the stigmatic surface of the carpel is a more precise site for pollen reception.
At the post-pollination stage, also, shade and water deficit substantially decreased carbohydrate accumulation by the endosperm and nucellus tissues (Fig.
The ovules of Rapateaceae are also remarkably similar to those of Dasypogon and Calectasia, exhibiting a massive starchy nucellus (Venturelli & Bouman 1988; see also Rudall 1994; Rudall & Chase 1996).
The term perisperm is a term used for the remains of the nucellus in dicotyledonous seeds (Fahn 1982) and could be used for the remains of the nucellus covering the micropylar end of the female gametophyte, but not for the pleurotesta.
In 75 % of the aberrant ovules, a portion of the nucellus was exposed and no micropyle was present.
soft layer fused with the nucellus which forms the pachychalaza.
Crane and Carman (1987) hypothesized that regulatory substances from the nucellus diffuse through the callose-deficient MMC, interfer with meiosis, and induce a mitotic-like division.
As the embryo develops, it becomes torpedo shaped, grows two cotyledons, and absorbs the endosperm and eventually the nucellus to occupy nearly all of the space within the ovary wall.