More membranes

​There are more membranes beyond those of endoplasmic reticulum in all living corn cells.  The nuclear membrane surrounds the nucleus.  Like other membranes function, it not only contains the contents but also regulates the movement of materials to and from the outside.  Messenger RNA is coded by the DNA in the nucleus and moves through the membrane to the ribosome with code for next protein.  Ribosomes, mitochondria and plastids (including chloroplasts) are largely composed of membranes.  A cell membrane surrounds all cytoplasm of the cell between the cell wall and the cytoplasm.  It also functions to regulate transport of materials in and out of the cell.
 
Cellular membranes consist of a few layers of lipids and proteins.  They do degenerate (age?) and require maintenance to replace or repair damage to the membranes.  Each of the living cells in a corn seed embryo includes multiples of membranes.  Drying of corn seed does cause some shrinkage of membranes and apparently causes membrane damage.  Sudden swelling of the cells with hydration can further damage the membranes.  Self-repair occurs but does require adequate heat for metabolism to supply the materials for repair.  There is some evidence that temperatures below 50°F for the first 24-48 hours after hydration results in permanent damage to its function because membrane damage from imbibition is not repaired.  If those first hours are warmer, adequate membrane repair occurs to allow normal embryo growth.
 
Cold germination tests are intended to detect the percent of seed within a seed sample with vulnerability to imbibitional chilling.  Some of those damaged may eventually germinate but later than others within the sample.  This could cause uneven emergence in the field if soil temperatures suddenly drop immediately after planting.