My first plant physiology course was taught by Professor Loomis in 1960 (oops, I just revealed my age). He told of having a debate with his wife while in the car in the Rocky Mountains as to whether they were going uphill or not, the surrounding terrain causing confusion. He claimed that he got out of the car and poured water on the road to prove the direction of the hill. “Water runs downhill” humph- he had the habit of loudly clearing his throat when he was making a major point. Water moves through cell membranes from a high concentration of water towards the lower concentration of water. High concentration of water equals less concentration of solutes. This process of osmosis is passive transport and is the main means in which water is moved from the soil through the living cells of young root tissue. Many of the minerals, however, require energy to move through the membranes to reach concentrations greater than that in the soil.
The living cells of the roots surround the xylem cells that form a fine tube to the stem tissue. These cells are ridged and dead when mature. Water is imported through the living cells into the xylem because the water moves from high to low concentration. Water molecules attract each other by sharing hydrogen bonds, causing the capillary action and movement of water from the root xylem to stem and leaf tissues. It spreads throughout the plant’s xylem tubes and into all living cells, keeping them turgid and allowing metabolism to occur. Stomata on the leaf surface that open to allow CO2 intake (and photosynthesis) also allow water vapor to escape. For each molecule of water transpired, another water molecule is pulled up the xylem. The corn plant is in need for constantly pulling in more water and the need increases as transpiration increases during dry windy days. It is also important that the chain of water molecules in the upper root tissue and lower stem is not broken to ruin the capillary action within the xylem tissue. Action above the ground is very dependent on the ability of the root tissue to absorb and transport water. Function of the root tissue is dependent upon the energy transformed in leaves and transported to roots.
Water does run downhill and is pulled up hill. Humph. I am sure Professor Loomis said that too but it was a long time ago and I forgot that part.
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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.