Membranes and germination

Germination of a corn seed depends upon a rapid metabolic change in the cells from the minimal respiration occurring in dry seed to cell elongation in the root (radical) and shoot cells.   This requires mitochondria to activate after the seed imbibes water.  Rapid swelling of the mitochondria may cause breakage of the membranes but they do have the capacity to self repair.  Energy supplied by heat affects the rate of metabolism in seed and thus the rate of membrane repair.  Seed with significant membrane injury upon imbibition are slower to repair under cool soil temperatures than in warmer soils.  The delay in repair may be so severe that no germination occurs.
 
There is evidence that too rapid of swelling leads to more membrane breakage and consequently physical breakage of the pericarp allowing water to be imbibed faster and that is linked to germination reduction. Furthermore there is some evidence that seed treatments that reduce the rate of swelling can improve rate of germination in some seed lots. 
 
Each seed in a seed lot may be genetically alike but they had an individual history.  They differ in location in the seed field, time of pollination, health of the parent plant, moisture at harvest, placement in the drying bin, physical injury during shelling and handling, drying temperature and actual speed of drying.  They also vary in position of the ear that affects maturity and shape of kernel. The latter affects the position of the embryo in relation to the endosperm.  The trend of round seed with its protruding embryo to have lower germination rates than flat seed is believed to be due to increased vulnerability to physical damage during handling.  Given all of these variables it is amazing that we even get 90% germination in the field.