I recall a phrase used by the plant physiology professor in a lecture that he used to make a point. While traveling through mountains, he was arguing with his wife as to whether they were going up hill or down, confused by surrounding terrain. He claimed he got out of the car and poured water on the road to see which way the water flowed. Then, he made the point to the students “water runs downhill!”.
Moisture from soil moves into the drier tissue of the planted dry corn seed. This imbibition causes the membranes of cells and their contents to expand, sometimes damaging the membranes. Cellular membranes have the ability to self-repair, but this process occurs more quickly with heat energy. Fast movement into the seed under cold soil conditions can cause significant damage to cell function ultimately resulting in slow or no germination.
Movement of water into the seed is slowed by the outer layer of cells in the pericarp. Breakage of this layer, results in more rapid uptake of water by the seed, potentially inhibiting seed germination. Seed treatments include a polymer coating to slow the uptake speed of water into the seed, allowing for membrane repair even when planted in cooler conditions.
Small breaks to the outer layer of cells in corn seed is practically unavoidable during the movement of harvested seed, despite extreme care of the seed producer. Ultimate uniform and nearly complete germination of the seed is enhanced by polymers applied to the seed outer layer. The warm germination test distinguishes seed sufficiently injured that cannot recover but the cold test identifies seed that cannot recover under the usual cooler soil conditions common for temperate zone corn planting. Pericarp cells, derived from the female plant, have some influence affecting the speed of water imbibition. Coating of the pericarp with a polymer can slow the imbibition process and resulting in less membrane damage.
Imbibition does not require living cells but simply the physical act of water moving down hill.
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.