Corn seed, dead or alive, will allow water to enter through the pericarp, causing the kernel to swell. Dry cells in the embryo retain many membrane-bound structures including mitochondria, plastids including chloroplasts, nucleus and endoplasmic reticulum. Cellular membranes are composed of phospholipids and proteins organized in a manner that regulates the biological function of the cell organelles including regulation of movement of products in and out of the organelle.
Membranes in a dry corn seed cell are only slightly active, oxygen to pass through, for example but have more of a gel like structure. Within a few hours of imbibition, the structure changes as the phospholipids become moist and swollen. Resulting metabolism with activation of respiration in mitochondria, fueling gene translation in the nucleus, movement of RNA on the endoplasmic reticulum and production of protein in the ribosomes. The water plus metabolism causes the radical part of the embryo to elongate and the germination process has begun.
Two potential problems can stop this process. The seed may no longer have sufficient structural integrity, possibly because the aging process while dry no longer maintained the metabolism needed for maintenance. A second problem can be that the imbibitional process caused breaks in the membranes that were not adequately repaired during those first few hours of swelling as water moved into the cells. Membranes do have the capacity to self-repair and often do when metabolism is active. However, this process is temperature related, and in corn this repair process is very slow when temperatures are at about 50°F. Imbibitional chilling injury is the term used to reflect poor germination of some seed when planted in cold soils.
Every seed within a lot, although genetically identical, has had a slightly different environment experience. Location on the ear, exposure to insect or fungus, location in the drier, handling in the sheller or bagging processor all could affect its tendency to cellular injury. This usually if most profoundly expressed when it imbibes water under cold conditions. Some seed may reflect this by only delaying the germination as it repairs sufficient membrane for metabolism to germinate although later than the other seeds.
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.