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Toluidine Blue Staining of Arabidopsis Pistil Sections

image of ovulesimage of ovules
Ovules are found in two chambers within the pistil, one on either side of the central septum.  The ovules are connected to the septum by a stalk called a funiculus. The orientation of each ovule relative to the axis of the pistil is random.
image of mature ovuleimage of mature ovule
Anatomy of a mature ovule.  These two ovules are oriented ~90 degrees relative to each other.  The funiculus (F) is attached to the ovule at the chalaza (C), where all the pieces of the ovule meet.  The outer (O) and inner (I) integuments each are comprised of 2 layers of cells, and they grow up around the nucellus (N) and meet at the micropylar end - this is where the pollen tube will enter to fertilize the egg.  The nucellus surrounds the embryo sac, and is highly asymmetrical: on one side (the left side in the picture on the right, and out towards the viewer in the picture on the left) it is thick, and the cells overlap like scales.  On the other side it is thin, and the embryo sac is pressed up against the integuments without any empty space.

Female Gametophyte (Embryo Sac) Development

For a schematic overview of embryo sac development, return to the overview page.
image of young ovuleimage of growing ovule
A young ovule with a megaspore mother cell prior to meiosis. The funiculus is at the lower left. Just beyond it are the two integument primordia, and beyond those is the nucellus, which holds the large megaspore mother cell.A growing ovule just after generation of the female gametophyte via meiosis. The outer (O) and inner (I) integuments are growing up from the chalaza (C) and will soon surround the nucellus (N)
image of megaspores after meiosisimage of a functional gametophyte
A closer view of the megaspores after meiosis. The asterisk marks the presumptive functional gametophyte, now at developmental stage FG1. (N) indicates two nonfunctional megaspores that are beginning to degenerate (note slightly emptier look).  Soon they will collapse into the the dark material to the right.  The chalazal-most megaspore is always selected as the functional megaspore.A functional gametophyte at stage FG1 (dark nucleus) surrounded by two layers of cells in the nucellus and and the partially completed inner and outer integuments. sectioning is in this image is oriented ~90 degrees relative to the axis of the ovule as compared to the image above. Click here for an electron micrograph of an FG1 embryo sac
image of stage FG3 embryo sacimage of an ovule with stage FG4 embryo sac
A stage FG3 embryo sac. The growth of the central vacuole has pushed the two nuclei to opposite ends of the syncytium.An ovule with a stage FG4 embryo sac. Two syncytial nuclei are visible adjacent to each other in the plane of sectioning, indicating that the second round of mitosis has occurred.
image of stage FG5 embryonic sacimage of embryo sac after cellularization, stage FG5 or FG6
One end of a stage FG5 embryo sac just prior to cellularization. Three syncytial nuclei are visible in this section. Closer view (electron micrograph) of this embryo sac.An embryo sac after cellularization, stage FG5 or FG6.  individual cells are visible at both ends of the gametophyte, separated by the large vacuole that is now contained within the central cell.

More images of toluidine-blue stained pistils.

Return to overview of embryo sac development.