Maize hormones

​Major growth regulation in corn is done with hormones.  There are three major types: cytokinins, auxins, and gibberellins.  Each has specific functions in the metabolism and growth of the corn plant. 
 
Cytokinins, originally produced in the corn seed scutellum, migrate to the root tip where they stimulate cell division.  Later, cytokinins trigger the cell division in all the growing points of the corn plant. These include the lateral root tips, the stem meristem and each of the lateral stem buds, including the one (or more) that becomes the ear.  Cytokinins also are active in delaying senescence of leaf tissue. Zeatin is a common cytokinin in corn and other plants.
 
Auxins influence cell elongation, stimulating it in stem cells but inhibiting it in root cells.  Auxins inhibit elongation of lateral buds countering the cytokinin effect of cell division.  It is the balance of the two hormones that affects corn plants tendency to tiller. The most common auxin is indole-3-acetic acid (IAA). Apical dominance in plants is controlled by this auxin.  This auxin also influences flowering and inhibition of abscission layers at the base of leaves and maturing kernels. Herbicides such as 2,4-D and dicamba are auxins that disrupt plant growth and development.
 
Gibberellins include more than 100 compounds that effect shoot elongation, seed germination and maturation of grain. These hormones are produced in root and stem meristems as well as tips of new leaves and seed embryos. Gibberellic acid is the most common compound that can be artificially added to plants.   Gibberellins tend to delay  kernel maturation and are effective in determining plant height.
 
Synthesis of these hormones is determined by genes, of course.  Plant height of different varieties involves these genes as the hormone synthesis involves several steps, with a few major genes causing dwarfness, and multiple genes affecting slight differences in plant height. Nearly all aspects of corn plant growth is affected by hormones.
 
Soil microbes also produce auxins and cytokinins that can affect root development and ultimately affect phosphorus uptake by changing the balance of hormones in roots.  Potential microbial seed treatments attempt to use these interactions to stimulate early corn growth.