Why is root hair important

Root hairs

© Jochen Euler
In botany, rhizodermis is the name given to a thin tissue covering a plant root. Alternative names are root skin and epiblema. In addition to the absorption of water and dissolved nutrients, the formation of root hairs is an important task of the rhizodermis.

Root hairs consist of a single cell that extends from the rhizodermis in a hair-like manner into the ground. The attachment occurs in a zone of high division activity, with a root hair usually emerging from a small protuberance (a papilla) at the apical end of the rhizodermis cells. The apical end is understood here to mean the end closest to the tip of the root. In many plant species the root hairs can form from all rhizodermis cells, in others the hair formation is limited to certain specialized cells (trichoblasts), which are distributed in a regular pattern on the surface of the rhizodermis. The application and growth (elongation) of the root hairs run synchronously in the individual root sections. The oldest hairs are the longest, and those closest to the tip of the root are the shortest.

Root hairs can only be found on young, growing roots. They are usually only viable for a few days to several weeks. They have a diameter of 5 to 17 micrometers and a length of 80 micrometers to 1.5 millimeters. Despite their small size, they serve to enlarge the root surface and improve soil penetration. Increased water absorption is possible through the root hairs. The surface for the absorption of water in the soil is therefore larger in most plants than the surface of the above-ground shoot, where the water is released through the leaves and evaporates.

Root hairs are in close contact with their environment and are often grown directly with the earth particles. When moving plants, the root hairs are usually broken off or damaged. The result is a lack of water for the plant in the next few days until new root hairs develop.
Not all plants have root hairs, for example all naked-seed plants have to do without these water-absorbing surfaces. Most of these plants, however, have developed protective mechanisms against excessive water evaporation, such as the coniferous family (Pinophyta).

The root hairs are surrounded by a carbohydrate-containing mucus that they release through the cell wall. This intensifies contact with their surroundings, the nutrient salts can already be prepared in this environment and then absorbed for forwarding.

In contrast to the root hairs, lateral roots are not formed from the root skin, but from the pericycle of the central cylinder. In addition, side roots do not grow positively geotropically (in the direction of gravity), but often at right angles to the main root.