Elongation of seed embryo radical becoming the primary root system is often the first to emerge from the seed. Geotropism causes it to turn downwards. Shoot portion of the embryo emerges with a hypocotyl with a shoot meristem at its tip. Its direction of growth upwards is also part of the geotropism phenomenon. The timing of the growth in each direction is affected by heat energy and efficiency of the metabolism in the embryo cells. That energy is stored in the endosperm and translated into metabolic energy by the cell mitochondria. Deterioration of the cells through aging, moisture imbibition and physical damage to the corn embryo can affect the efficiency of these initial growths from the seed. Warmer temperature can minimize the damage by increasing the repair of damaged membranes in the cells.
Primary root growth has limited life as the seed source of energy is depleted. Hypocotyl upwards push towards soil surface until it detects far red light close to the soil surface. The final emergence coincides with emergence of the first collared leaf. This followed by a series of leaves. These leaves provide the energy not only for development of new green tissue but also the energy for new secondary roots growing from the first node of the stem at the base of the shoot in the soil. At this time the energy from the seed endosperm is no longer utilized as the primary root deteriorates.
The process for successful shoot emergence is dependent upon seed quality factors including genetics, especially of the female parent as the main supplier of mitochondria genetics, seed damage, field conditions including temperature.
It is amazing that the complex process is usually successful.
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.