Expert: Dana Krempels, Ph.D. - 5/5/2011

Question
My biology textbook says that a megaspore cell in an angiosperm divides by mitosis three times to form eight nuclei. Six of these form plasma membranes through cytokinesis to create an embryo sac. Then it says there are three cells at one end (the egg and two synergids) and three at the other (antipodal), with two more in the middle (polar nuclei). Do the cells at either end not have nuclei, or are they part of the plasma membrane? Thanks.

Answer
Dear Brian,

The megagametophye (the eight-nucleate sac) is actually NOT composed of cells.  It is a single mass of cytoplasm with eight nuclei (not cells), just as you have described.  The embryo is said to be syncytial: a shared mass of cytoplasm with multiple nuclei embedded in their respective locations.

Hope that clears up the confusion.  (If the textbook really says that the synergids, ovum, antipodals, and polar nuclei are cells, then it's not a very good textbook.)  :(

Hope that helps.

Dana