Chromosomal DNA from both parents of a hybrid influence the early growth of a germinating corn seed. However, the female parent has more affect then the male. It begins at pollination, in which the ovule is encased in the ovary wall destined to be the pericarp of the grain, making it a fruit with a single seed. This is totally composed of the cells of the female plant. Ovule cells of the female divide 8 haploid cells, one of which is the egg cell and 2 that become ‘polar cells’. Pollen contributes two haploid sperm nuclei, one fusing with the egg cell nucleus leading to the diploid embryo development and one fusing with the two polar nuclei and eventual formation of the triploid endosperm. The male contributed chromosomal DNA but the female parent also contributed important cell organelles such as mitochondria and plastids, including their DNA. The female parent contributes structure of the pericarp, two-thirds of the chromosomal DNA of the endosperm and the two important components of the cells.
Stress from drought, high temperatures or reduced photosynthesis during early days of grain fill are often associated with reduced germination percentage of maize seed. There is evidence that these stresses affect the balance between cytokinins and abscisic acid, the latter remaining at a high concentration and consequently reduced cell division in the developing endosperm. This results in fewer cells in the endosperm for storage of starch, affecting seed size but the effect on germination is not clear. Does shrinkage of endosperm put stresses on the pericarp, resulting in damage to the outermost layer of the corn kernel and consequential rapid imbibition?
Mitochondria in the endosperm and embryo cells can withstand considerable drying stress, as witnessed by the effect of rapid drying after harvest. These organelles maintain life in the dehydrated state until activated with imbibition of water during germination. This is essential for them to provide chemical energy stored in the endosperm into growth of new cells in the embryo. Mitochondrial function is dependent upon membrane activity. Damaged membranes can repair under warmer conditions but not when soil temperatures are cold. Rapid imbibing of water can cause damage to membranes. Physical damage to kernel during harvest or after drying can damage the pericarp and other seed cells, resulting in fast imbibition as well.
Hybrid chromosomal DNA affects many aspects of germination but female components are predominant, before and after harvest, on the vulnerability of the seed to germination. Potentials for producing less-than perfect seed are many. The art and skill of seed producers and the many others involved in maximizing the conversion of an ancient plant like Teosinte into an efficient converter of sunlight into useable form of chemical energy is amazing.
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.