Maintaining high quality seed
Mitochondria are not the only membrane source in corn seed cells. Nearly all cell functions are carried out on membranes. Endoplasmic reticulum (ER) is a major component of the cell which acts as transporter of the enzymes and proteins being produced in the cells. It is also the transporter of the messages from the DNA in the nucleus of the cell. Virtually all cell functions are dependent upon the structure of cell membranes.
Development of membranes in seed is dependent upon a combination of the genetics of the variety and the environmental stresses during seed development. Drying the seed also significantly affects the membranes, as the membranes collapse with drying. Corn seed producers are very aware of this potential problem and develop methods to assure that seed drying is carefully monitored so handling is gentle. Seed membrane deterioration can occur in the field, especially if seed is allowed to dry slowly after fully developed at about 35% moisture when the abscission layer (black layer) cuts off nutrition from the plant. Rain preventing harvest at this critical time is one cause of loss of seed viability because it begins an aging process in corn seed.
A combination of drying temperatures below 100°F and quick drying by high air movement is critical to maintaining membrane integrity in corn seed. Although all cellular membranes are probably affected by drying conditions, the fact that germination deterioration is mostly linked to the female parent of a hybrid, it is likely that the mitochondrial membranes are affected the greatest. Each corn genotype varies somewhat in tolerance to these factors, but the principles of drying temperatures and speed of drying appear to mostly involve membrane deterioration. There is also some effect on the pericarp of the grain if it causes breakage. Seed producers apply this knowledge and a lot of art to balance all the variables involved in producing seed with high field emergence rates the following spring.
Respiration of dried seed is needed to maintain membrane integrity while being stored but low temperature and dry atmosphere is needed to minimize the activation of excessive seed metabolism. The combination of seed moisture no greater than 13% and the temperature of 50°F and 50% relative humidity is usually considered adequate for maintaining seed germination quality for several months. Genotypes vary in maintenance of seed quality even in this environment. Stresses during the growing season also can cause some seed to deteriorate even with careful storage monitoring.
Production and maintaining high quality corn seed requires corn genetics, non-stressful growing environment, careful handling at harvest, drying and shelling and proper storage before the next planting season. There is an art to being a good seed producer.
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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.