In botany, we denote by rhizodermis a mostly single-row tissue of a plant root. Alternative names are root skin, Epiblema or root epidermis. In addition to the absorption of water and dissolved nutrients the formation of root hairs and thus the significant increase in the absorptive root surface is an important task of rhizodermis.
Like the epidermis in the aboveground plant organs lying shoot and leaf is the rhizodermis usually only a series of, in contrast to the epidermis, nichtcutinisierten cells. Below the rhizodermis the hypodermis connects to an approximately equal thick layer of rugged, longer-lived and sometimes slightly corked cells.
Root hairs consist of a single cell, which extends from the rhizodermis hair shaped in the ground. The investment is made in the area of a zone of high mitotic activity, with a root hair usually ( a papilla ) can be seen from a small protuberance at the apical end of the Rhizodermiszellen. Under apical end is meant here is the tip of the root nearest the end. In many plant species, the root hairs can form from all Rhizodermiszellen, in others the hair formation is restricted to certain, it specialized cells ( tricoblast ) that are distributed in a regular pattern on the Rhizodermisoberfläche. The investment and growth ( elongation growth ) of the root hairs are synchronous in the different root sections. The oldest hairs are the longest, the nearest the root tip, the youngest.
Surface and water absorption
Root hairs are found only in young, growing roots. They are usually only a few days ( three to nine days) viable. They have a diameter of 5-17 microns and a length of 80 microns to 1.5 millimeters. Due to the mass of formed root hairs, with a rye plant, for example, approximately 10 billion root hairs of 10,000 km Total length, there is a significant increase in the resorbable root surface. Since root hairs exhibit a peak growth, they are the root in better penetration of the ground to help. Through the root hairs increased water intake is possible. The receiving surface of water in the soil is thus higher than the surface of the aerial shoot to which the water is discharged through the leaves of most plant and evaporated.
Root hairs are in close contact with their environment and are often fused directly to the soil particles. When converting from plant root hairs are usually broken or damaged. Lack of water for the plant in the next few days until the formation of new root hairs result.
Not all plants have root hairs, so about every Nacktsamigen plants must survive without this water absobierenden surfaces. Most of these plants have not yet developed protective mechanisms against excessive evaporation of water, such as conifers ( Pinophyta ).
Uptake of nutrient salts
The root hairs are surrounded by a carbohydrate -containing slime, which they leave on the cell wall. Thus, the contact with their surroundings is intensified, the nutrient salts may be already prepared in this environment and then taken for forwarding.
Lateral roots are formed in contrast to the root hairs not from the root skin, but by the pericycle of the central cylinder from. Moreover grow lateral roots not positive geotropic ( in the direction of gravity ), but often at right angles to the main root.