Corn fields in Northern Illinois are showing corn seedlings this past week. Planting was a little late this year because of wet soils. Seeds imbibed water nearly immediately after planting. Heat provided the energy for initiating the activation of metabolism within the cells. Activation of enzymes already present in the cells assisted in the respiration process in which glucose was used to produce ATP (adenosine triphosphate). This energy, combined with components of the glucose molecules, nitrogen and phosphorus molecules produced more enzymes, some of which triggered production of RNA (ribonucleic acid) coded by the DNA (Deoxyribonucleic acid) in specific genes of the chromosomes. RNA molecules were transferred to the ribosome organelles in the cells where the nucleic acid codes attracted specific amino acids hooked together in long chains as new proteins. Some of these proteins were specifically coded to become enzymatically active in other metabolism, including production of more cell growth.
Cell growth, largely by cell elongation, pushed the root tissue downwards and the shoot tissue upwards. Initial shoot elongation occurred in the hypocotyl but as the apical meristem reached about ½ inch of the surface absorption of light stimulated that elongation to stop, and the rapid growth of the cells in leaf tissues near the apical meristem. The first of these leaves, the coleoptile, wrapped tightly around enclosed 5 or 6 leaf primordia, continued pushing through the soil as cell elongation continued. Growth to this stage was the result of water absorption providing pressure for cell elongation and energy derived from stored starch in endosperm, translation of DNA into enzymes and production of new cellular parts and cell walls.
Further exposure to light after emergence resulted in some plastids within the cells of leaves, including that small coleoptile, to produce chlorophyll. Photosynthesis in these chloroplasts is the beginning of dependence on energy from the seed endosperm. Chloroplasts, influenced by their own DNA, inherited through the female parent of the corn plant, and the DNA of the cell nucleus react to environment including light intensity, heat, minerals in soil and chemical additives. Chloroplast function contribute to the cell growth, as more leaves emerge from the soil with growing momentum.
We are accustomed to seeing the result of corn breeders’ selections of genetics that work in expected environment. Most of us do not see the results of genetics in which the above process fails. We also hope to not witness the cases where the environments failed to support this process, with insufficient oxygen in water-logged soils, misapplied herbicides or poor fertilizer application. Usually we only see the remarkable result of coordination of cellular activity when a corn seed germinates, and a seedling emerges.
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.