Development of ovule, embryo sac and endosperm in Brodiaea (Liliales).
Development of ovule, embryo sac and endosperm in Dipterostemon and Dichelostemma (Alliaceae) relative to taxonomy.
Megasporogenesis and embryo sac development in Calochortus.
It was originally coined to define a route involving sexual reproduction, egg fertilization, and subsequent inactivation of the female nucleus, so that a male-derived, haploid embryo is formed within the embryo sac (Rieger et al.
However, and as a difference with recent reviews, I will pay special attention in this review to the other two, less known alternatives: male-derived haploid embryogenesis within the embryo sac, and meiocyte-derived callogenesis.
Male-Derived Haploid Embryogenesis in the Embryo Sac
The literature registers many functions for the hypostase: it may act as a barrier tissue for stopping the encroachment to the embryo sac
; it may connect the vascular supply with the embryo sac
and, thus, facilitate transport of nutritional material; it may be responsible for the production of certain enzymes or hormones, among others (TILTON, 1980; BOUMAN, 1984).
Earlier, the research team used genetic tools to shift the position of a single nucleus at one end of an embryo sac in the plant Arabidopsis.
After multiple tests, the researchers found that during embryo sac formation, auxin concentrations did indeed follow a gradient, with the highest levels occurring in the ovule at the end of the embryo sac where the pollen enters and lowest levels occurring at the opposite end of the sac.
They confirmed their hypothesis after varying auxin concentrations in the embryo sac of the plant.
fournieri, also known as the wishbone flower, makes a good model system because its ovaries, or embryo sacs
, protrude from the base of the flower, Tetsuya Higashiyama of Nagoya University in Japan and colleagues note in the new study.
In one aspect of this work, the scientists are investigating how such messages may help the growing pollen tube find its way to the embryo sac.
To find out, her team is determining the makeup, or DNA sequence, of genes that are switched on or off in the male cells and in the embryo sac cells.
Even though the extra fertilized egg later dies off -- and the nonflowering Ephedra's embryo ultimately feeds on its embryo sac cells -- Friedman says this is evidence of how endosperm once formed.
Paleobotanists surmise that before the advent of endosperm, all growing plant embryos fed on cells from their embryo sacs -- the maternal tissue that gives rise to unfertilized eggs.