Hormones in corn

​Corn has been selected by humans from the wild plant Teosinte to move more carbohydrates than is needed for not only plant reproduction but to also store excessive amounts in form for human consumption. This over-production is a metabolic process that goes on after pollination as it shifts in the flow of sugars within the corn plant changes.
 
​Corn plant growth is greatly affected by a broad class of complex chemicals called hormones. Two of the kinds of hormones related to grain fill are the cytokinins and abscisic acid (ABA).  These two hormones have opposing functions in plants, including the development of corn kernels.  Cytokinins function is to increase cell division and delay senescense of tissue.  They are produced in roots and transported via the xylem to meristems such as in each kernel. They also may be produced in seed embryos also but evidence for that is elusive.  Regardless, cytokinins accumulate in developing seeds where they are responsible for stimulating cell division.  Cytokinins are also linked with the transportation or at least the attraction of sugar to the developing kernels.
 
Abscisic acid, on the other hand, is associated with cutting off of translocation to tissue basically by causing a layer of thick-walled cells impervious to movement of materials.  Abscisic acid production increases when the plant is stressed. The black layer at the base of mature corn kernels and at the base of husk leaves in a mature corn ear are stimulated by abscisic acid. 

Freshly pollinated ovules have a balance of these two hormones.  A non-stressed corn plant normally has a balance favoring the cytokinins stimulating more cell division and, consequently, flow of sugars to the individual kernels.  However, if the plant is under heat or drought stress the balance tends to favor abscisic acid.  The affect can be abortion of those kernels.  Corn kernels within the first 10 days after pollination are most vulnerable, perhaps because the accumulation of cytokinin is too great to be overcome by a short-term increase in abscisic acid.
 
Genetics and environments influence the production of these two critical hormones affecting grain yield in a corn field.