The corn embryo is alive but dormant until water is imbibed. The water causes membranes in the cells to activate. Mitochondria absorb the surrounding carbohydrates and those coming from the endosperm via the scutellum. RNA, some of which is newly transported from being coded by the DNA in the nucleus is translated in the proteins needed for processing the sugars into the chemical energy ATP. This energy, and that provided by heat, is utilized for cell division and elongation in the root and shoot meristems.
Root tip cells are surrounded by a special layer of cells (coleorhiza) that act as a protective covering when the root tissue, also called the radical, pushes through the pericarp of the seed. Root tips include special cells with organelles (statoliths) that are heavier than other parts of the cell. Consequently, they accumulate on downside of the outer layer cells of root tissue. These cells lead to production of hormone-like chemicals (auxins) that inhibit root cell elongation on the lower side of the emerging root. With greater cell length on the upper side, the root grows downwards, regardless of the orientation of the seed when planted.
This initial root is called the primary root. It is usually unbranched and relatively short lived as secondary roots grow from the lower nodes of the stem portion of the embryo. Between the two major parts of the corn embryo between these two is the mesocotyl.
The shoot portion of the embryo already has several nodes, each with undeveloped leaves. Energy and water stimulate cell growth and division in the meristem causing the shoot to push through the pericarp usually after the primary root has emerged and begins absorbing soil moisture and minerals from the soil to be transported to the shoot.
Shoot tips cells also produce similar organelles also affected by gravity. They also produce auxins, but these hormones have the opposite affect on shoot cell elongation. Those cells on the gravity side with more auxin become longer than those on the upper side. Consequently, the shoot grows upwards.
Affect of gravity on plant growth direction is called geotropism. After shoots emerge, phototropism becomes dominant, causing the plant to grow towards light because cells on the shaded side produce more auxin and consequently longer cells.
When all works as planned healthy seedlings begins the season.
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.