Germination process begins when sufficient temperature allows metabolism in the imbibed seed. Energy transformed from the carbohydrates in the endosperm, through active mitochondria, allows the cell elongation in the root and the shoot portions of the embryo. Geotropism and auxins guide the root downwards and the shoot upwards as the cells elongate. The shoot apical meristem is pushed upwards as the cells away from the tip elongate forming the mesocotyl. This continues until the tip is exposed to the red wave length of sunlight a short distance (one inch?) below the soil surface. This light affects production of plant hormones resulting in stopping the elongation of the mesophyll cells, inducing production of the first node, with elongation of the coleoptile to push through the remaining soil. That first node becomes the site for production of the secondary root system, as everything below that node eventually deteriorates.
The coleoptile, forms the ‘spike’, that emerges through the soil surface, the cells of leaves within it elongate, forcing the coleoptile to split. The first true leaves unfurl and emerge. The first leaf is not shaped like the rest of the leaves, being shorter and growing more horizontal. It does provide the beginning of independence from the nutrition supplied by the seed endosperm. This first leaf will be discarded later as its energy is depleted supplying energy for the growth of the next leaves.
Photosynthesis in the next few leaves provides the energy for more leaf emergence as well as the new secondary roots as they grow from that first node slightly below the soil surface. The rate of growth of this early stage is very dependent upon temperatures. In our greenhouse with a minimum soil of 70°F, the third leaf has emerged in about 9 days but with usual spring days in Central USA it can be 20-30 days before the third leaf is obvious.mmGenotypes vary in speed of this early growth but temperature is the major variable.
Success at this stage is essential for a productive crop. Good genetics, seed quality and cooperating environment gets the corn off to a good start.
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.