Root System: Detailed Analysis of Roots, Characteristics, Types and Regions of Roots

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Characteristics of Roots

Non-green due to absence of chlorophyll, not divided into nodes and internodes, positively geographic (grow towards gravity), positively hydrotropic (grow towards water), negatively phototropic (grow away from light), Lateral roots are developed from an inner layer (i.e. pericycle) and unicellular root hairs present just behind the root caps which increase the absorptive surface area of roots.

Types of Root Systems

Root systems are mainly of two types.

Tap Root System

A root system with a prominent main root, directed vertically downwards bearing small lateral roots. It is characteristic to dicot plants, e.g. carrot, radish, rose, trees etc. Tap root is primary in nature as it is formed from the radicle.

Fibrous Root System

A root system that develops from the base of the plumule (hypocotyl) in which all roots are equally prominent. They do not branch profusely, are shallow and spread horizontally, hence cannot provide strong anchorage. Fibrous root system is the main root system of monocots, e.g. maize, grasses, wheat.

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Types of Roots

There are two types of roots;

Tap Root

It is the primary and the main root that develops from the radicle, bears many branches and remains underground. It is usually found in dicots, e.g. sunflower, mustard, carrot and mango.

Adventitious Root

These are roots that develop from any part of the plant except the radicle. They may arise from the underground or aerial stem or from leaf margins. They may grow from node (money plant, bamboo), stem cutting (rose), tree branch (banyan) or stem base (fibrous roots in monocots).

Regions of Root

Regions of roots are as follows.

Root Cap Region

Root cap is a thick, cup/thimble-like structure that protects the tender root apex. Cells of root cap secrete mucilage, which acts as a lubricant and helps the root to penetrate the hard soil.

Region of Meristematic Cells

Just above the root cap and cells are very small, thin-walled, densely protoplasmic and actively dividing, hence this can also be called as the region of cell division. It is about a few millimeters in length. By dividing and producing new cells, it adds to the longitudinal growth of the root.

Region of Elongation

It lies proximal to the meristematic region. Cells in this region undergo rapid elongation and enlargement and are responsible for the growth of root in length.

Root Hair Region

This region is about 1-6 cm in length and lies just above the region of elongation. Several cells of the outermost layer in this zone produce extensions, called root hairs which absorb water and mineral salts from the soil.

Region of Maturation

The cell of this region undergo differentiation/maturation into the cells of cortex, endodermis, pericycle, xylem and phloem and in permanent region (lies behind root hair) produce lateral roots, anchors the plant in soil and conducts water and minerals upwards.

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In maize root tip, Clowes (1958) discovered a central cup like reservoir of inactive cells lying between the root cap and the active meristematic region, called the Quiescent Centre. These cells become active whenever the previously active meristematic cells are damaged.