The root cap protects the growing parts of a root as the root grows through the soil

The tips of most roots are covered and protected by a thimble-shaped root cap (fig. 7.5). Cells of root caps can secrete large amounts of mucigel, a slimy substance (fig. 7.6) containing sugars, enzymes, and amino acids. A root weighing only 1 gram can secrete as much as 100 milligrams of mucigel per day. Although this rate of secretion may seem rather insignificant, the total amount of mucigel secreted by an actively growing group of plants can reach impressive proportions. For example, the roots of 1 hectare (about 2.5 acres) of corn secrete more than 1,000 cubic meters of mucigel during a growing season; that's enough mucigel to fill a typical two-story, four-bedroom house.

Mucigel has four major functions:

  1. Protection. Mucigel protects roots from drying out. It also may contain compounds that diffuse into the soil and inhibit growth of other roots. For example, the mucigel of giant foxtail can decrease the growth of nearby corn roots by about 33%. What advantage might this be for the giant foxtail?
  2. Lubrication. Mucigel lubricates roots as they push between soil particles.
  3. Water absorption. Soil particles cling to mucigel, thereby increasing the root's contact with the soil. The water-absorbing properties of mucigel help maintain the continuity between roots and soil water.
  4. Nutrient absorption. Mucigel makes it possible for minerals, along with water in the soil, to be better absorbed by roots.
Mucigel Root

FIGURE 7.6

The outermost cells of root caps secrete mucigel, a polysaccharide that lubricates the tip of the root as it moves through the soil (X760). In this micrograph, mucigel surrounds the root cap of corn (Zea mays).

FIGURE 7.6

The outermost cells of root caps secrete mucigel, a polysaccharide that lubricates the tip of the root as it moves through the soil (X760). In this micrograph, mucigel surrounds the root cap of corn (Zea mays).

There is no structure in shoots that corresponds to a mucigel-producing root cap. What might be the evolutionary explanation for this difference?

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Responses

  • lisa frankfurter
    How does mucigel and the rhizophere assist the root in absorbing water and minerals?
    8 years ago
  • Peter Eberhart
    What are protects the roots as it grows through the soil?
    6 years ago
  • Girmay
    What protects the roots from enzymes?
    5 years ago
  • marmaduke
    What protects the root as it grows?
    4 years ago
  • Cinzia Ferrari
    Why is Root Cap slimy?
    2 years ago
  • Maria
    What do root caps secrete?
    1 year ago

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