Most hybrid corn fields in Northern Illinois are pollinating this week. Within the past two weeks, at least one lateral meristem emerged from one of the stem nodes. This meristem produces a series of modified leaves but eventually produces 500-1000 special meristems. Each of these modified meristems includes one ovule cell with a nucleus that includes one set of the 10 chromosomes inherited from each of that plants parents. These diploid ovule cells undergo meiosis resulting in 4 cells, each with only one representative of each of the 10 chromosomes, a random mix of some from each of the two original parents. Only one of the 4 haploid cells resulting from meiosis develops into a megaspore cell, as the other three degenerates. These megaspore cells not only have the haploid nucleus but also other cell components such as mitochondria (and their DNA), plasmids and ribosomes.
The single megaspore cell undergoes three successive mitotic divisions, resulting in 8 nuclei, all haploid. This megaspore cell thus becomes an embryo sac containing 7 cells, as two nuclei are included in one of the cells. That cell within the embryo sac is destined to become the endosperm after pollination. One cell at the base of the embryo sac becomes the egg cell. Other cells within the embryo sac apparently participate in pollination only by producing hormones to attract the sperm cell from the pollen tube to the egg cell.
Elongation of special tissue at the outer tip of each embryo sac begins to elongate, to emerge from the surrounding leaves. These structures known as silk become the channel for eventual entrance of the pollen nuclei.
About Corn Journal
The purpose of this blog is to share perspectives of the biology of corn, its seed and diseases in a mix of technical and not so technical terms with all who are interested in this major crop. With more technical references to any of the topics easily available on the web with a search of key words, the blog will rarely cite references but will attempt to be accurate. Comments are welcome but will be screened before publishing. Comments and questions directed to the author by emails are encouraged.