Plant Root System - Lecture 5 PDF

The Root system Roots are the underground part of all vascular plants. Root is responsible for anchoring the plant into the ground and absorbing nutrients, and water from the soil. There are two types of roots according to their origin: 1- Tap root It originates from the radicle in t...

The Root system Roots are the underground part of all vascular plants. Root is responsible for anchoring the plant into the ground and absorbing nutrients, and water from the soil. There are two types of roots according to their origin: 1- Tap root It originates from the radicle in the embryo. Tap roots have a main central root (primary root) upon which, smaller, lateral roots (secondary roots) are attached. 1 Types of tap root A) Normal tap root B) Storage tap root: The primary root of the tap root becomes fleshy and swollen due to the stored food. There are three types of fleshy tap root: Conical root: it is conical in shape, i.e. widest at the top and tapering steadily towards the bottom, e.g. carrot. Fusiform root: it is widest in the middle and tapers towards the top and the bottom, e.g. radish. Napiform root: It is very broad at the top and tapers suddenly like a tail at the bottom, e.g. turnip. 2 3 2- Adventitious root It originates from any part of plant other than the radicle. Types of adventitious root A- Fibrous Roots They arise in groups from the base of a stem or the nodes of a horizontal stem. They are thin and thread-like. The fibrous roots do not penetrate deep in the soil. B- Tuberous root They are thick and fleshy due to the storage of food e.g., Sweet Potato. 4 C- Climbing Roots These are non-absorptive roots which are found in climbers. They penetrate the cracks or fissures of the support. D- Parasitic Roots The roots occur in parasites for absorbing nourishment from the host. E- Respiratory roots Roots of plants growing in water-logged soil do not have enough oxygen for respiration. Thus, these plants produce special roots from the underground roots of the plant, which grow vertically upwards and help in gaseous exchange required for respiration. 5 F- Contractile root It is a thickened root at the base of a corm, bulb, or other organs. It shrinks under conditions of drought. Thus, it helps position this plant part at an appropriate level in the ground. G- Prop root It arises from the lower nodes of stem, grows downwards, penetrate the soil and provides mechanical support to the plant. 6 7 8  Anatomy of the root Dicot root shows the following regions in its transverse section as follows: 1. Epidermis - It is the outermost layer with several root hairs. It consists of thin walled, compactly arranged parenchymatous cells. It provides protection to the roots and due to presence of root hairs it also helps in absorption of water and minerals from soil. 2. Cortex - It is thin walled, multilayered region, made from parenchymatous cells. The cortex is responsible for transportation of water and salts from the root hairs to the center of the root. 9 3. Endodermis - It is the innermost layer of cortex. It consists of parenchyma without intercellular spaces. Most of the cells are characterized by the presence of special thickening of suberin and lignin on their walls called Casparian strips. Some endodermal cell near protoxylem has no Casparian strips and called passage cells. These cells allow diffusion of water and minerals through the endodermis. 4. Pericycle - It is the outermost layer of stele and composed of parenchymatous cells. 5. Vascular bundles - They are 2-8 in number and radial (xylem and phloem are found at different radii alternating with each other ). 10  Xylem is exarch (protoxylem towards the periphery and metaxylem towards the center) and consists of tracheids and vessels. Pholem forms oval masses beneath the pericycle, alternating with xylem bundles. Pholem consists of sieve tubes and campanion cells. 6. Pith - It consists of thin walled, parenchyma. It helps in storage of food materials. 11 T.S. in a dicot root 12 Features of monocot roots Epidermis It consists of thin walled cells with root hairs. Cortex is a multi-layered region of parenchymatous cells. Endodermis consists of barrel shaped parenchyma. Casparian stripes are little present. Pericycle is made from thin walled parenchymatous cells. Vascular bundles are radial, xylem is exarch, bundles more than six. Metaxylem elements are oval or circular. Pith is relatively large. 13 T.S. in monocot root 14