ANATOMY OF ROOT Consists of four zones: - The root cap - Zone of cell division - Zone of elongation - Zone of differentiation/maturation

ground meristem procambium

The Root Cap Consists of parenchyma cells that cover the root tip. The cells can be large or small, protecting the delicate or soft tissue behind it. Cells on the surface of the root cap secrete a slimy substance called mucilage, which accumulates in the cell wall and finally released. Besides assisting the movement of root tip through the soil, the slimy mucilage provides a conducive environment for growth of useful bacteria. Cells on the surface of the root cap which are eroded, are continuosly replaced from inside.

Zone of Cell Division   Consists of the apical meristem at the tip of root The apical meristem forms three primary meristems: a. Protoderm, that produces the epidermis on the outside b. Ground meristem, the part internal to the protoderm which produces the parenchyma cells of the cortex. c. Procambium, a solid cylindrical structure in the middle of the root, which produces the primary xylem and phloem.

Zone of Elongation This zone is situated above the apical meristem. In this region the cells are longer and broader than their original shape. At the same time, smaller vacuoles coalesce to become one or two large vacuoles that occupy 90% or more of the cell volume.

Only the root cap, the apical meristem and the elongation zone that push the root deeper into the soil. The region above the elongation zone is not involved, since the cells within do not increase in size anymore. Other parts of the root do not move, unless there is a cambium that will cause an increase in root size through the formation of secondary tissues.

Zone of Differentiation/Maturation In this region, the cells mature and differentiate into different cell types. The change includes roor hair formation through the elongation of the epidermal cells. Cuticle is formed on the root hairs and epidermal cells to protect the cells from attack by bacteria, fungal and other organisms, but at a thickness that allows the absorption of water.

The cortex region consists of parenchyma cells which mostly store food The cortex region consists of parenchyma cells which mostly store food. To the inside is the endodermis, consisting of a single layer of compact cells forming a cylinder.

Equisetum endodermis with casparian strip On the primary wall of the endodemis, there is deposition of suberin (a fatty substance) that forms the casparian strips on the radial and transverse walls. The plasmalemma of endodermis coalesce with the casparian strip preventing movement of water, except through plasmalemma without casparian strips. Dangerous heavy metals are prevented from entering the cell while beneficial ones are allowed in. Equisetum endodermis with casparian strip

The endodermal cell may become thick due to the deposition of suberin, wax, cellulose and occasionally lignin. To the inside of the endodermis is the vascular cylinder (stele). In between the vascular cylinder and the endodermis lies the pericycle region, consisting of one layer of parenchyma cells, or more layers in some plants.

Monocot root Dicot root

Cells of the pericycle continue to divide even at maturity Cells of the pericycle continue to divide even at maturity. Lateral roots and part of the vascular cambium of dicot plants are formed from the pericycle tissue.

In most dicot and conifer roots, the primary xylem consists of tracheids and vessels. The xylem forms arms that radiate towards the pericycle, and there can be two, three, four or more of such arms. In monocot roots, and a few dicot roots, the primary xylem encloses a central region of parenchyma cells, which is the pith. The xylem arms are not very prominent.

In the beginning, the cambium follows the shape of the primary xylem arms during the formation of secondary phloem on the outside and secondary xylem on the inside. Finally, the cambium position changes and the secondary conductive tissue forms a cylinder.

Secondary growth in root

Primary phloems that are located in between two primary xylem arms finally disappear when the secondary tissue increases. In roots of woody plants, a secondary cambium which is the cork cambium (phellogen) is formed from the pericycle to produce the cork tissue.