Maize, like all plants, has special structural adaptations to the chemical characteristics of water. Water molecules share hydrogen bonds with each other resulting in a cohesiveness between them. This plus a tendency for adhesiveness to certain xylem wall components allows for capillary action in the small xylem tubes.
Water moves from soil through the cell walls of the root by process of osmosis. Higher concentration of water outside the cells because of solutes such as minerals or sugar in the cell cytoplasm draws water into the root tissue mostly through the root hair extensions of the epidermal cells. The same physical phenomenon causes the water to move to the dead xylem tissue. Meanwhile, water on the surface of the mesophyll cells in corn leaves, exposed to open stomata, evaporates into the atmosphere. This also is due to the cohesive nature of water molecules as the moisture in the air has a lower concentration of water molecules than that between the cells beneath the open stomata. A small percentage of the water is tied up by photosynthesis and some is utilized as a medium of cell metabolism but most escapes through the stomata.
Because of the osmosis, water is pushed into the root cells and by cohesion-adhesion, every molecule of water lost through stomata is replaced by a molecule traveling to the leaf. Breakage of the capillary via insects or pathogens can cause a wilt in a small area of the plant but xylem lateral connections usually avoid complete wilting. For example, the northern leaf blight fungus Exserhilum turcicum plugs the xylem for a small area of the leaf making a wilted lesion of about 2-3 inches but is eventually stopped by the plant resistance system. Water moves around the wilted area and pulled up through the xylem tissue, some going via osmosis to living cells and most moving out into the atmosphere through stomata.
It is the molecular nature of H2O resulting in cohesiveness that leads to the push of water into the roots and the pull of water up and out of the corn plant.
Visit us at the ASTA in Chicago, Dec 9-12 (booth G207)
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.