Root system: – The root system is a non-green, underground descending organ of the plant that develops from the radicle section of the embryo. It has a positive geotropic and hydrotropic balance.
Root System Characteristics
1. The plant’s vegetative axis, which evolved from the Radicle component of an Embryo, is Descending.
2. It has positive geotropic, hydrotropic, and phototropic properties.
3. The root system is made up of three parts: primary root, secondary root, and tertiary root. A tiny root cap surrounds each root.
4. Unicellular root hair is produced by lateral roots. These are involved in water and mineral nutrition absorption.
The Root system has the following functions:
1. It anchors the plant body to the earth. (Fixation).
2. It draws water and minerals from the soil and absorbs them (Absorption).
3. It transports water and minerals to the system’s components. (Conduction).
The Different Types of Root Systems
The Root system is divided into two categories. 1) The Taproot System 2) fibrous Root system.
- Tap Roots
The Radicle grows into a single, central main root known as the ‘Primary root’ in the Taproot system. It grows lateral secondary roots that branch into tertiary and quaternary roots. Lateral roots have unicellular root hairs that help the soil absorb water and minerals. Taproot is a type of root that grows deep into the earth and stays with the plant for its entire life. Example Dicot plants
2. Fibrous roots
Radicle develops into the major root of the Fibrous root system. It’s short-lived, and a cluster of slender, fiber-like roots takes its place soon after. They have root hairs that aid in the absorption of nutrients. Fibrous roots do not grow deep into the soil (Surface feeders), therefore they must be replenished regularly. Example Monocot plants
Adventitious roots
‘Adventitious roots’ are roots that have formed in addition to the radical. They could be in the air or beneath. It can arise from any portion of the plant, including branches, nodes, and so on. It serves a variety of purposes, including mechanical support, food storage, and absorption. example Dicot and monocot plants.
Root System Modifications:-
Root modification refers to any alteration in Roots’ regular form and structure in response to a plant’s demand. Both taproot and adventitious roots are changed to perform unique roles like food storage, mechanical support, and to aid in vegetative proliferation.
I.Modification of Underground Roots.
II.Taproot and Adventitious Root are both modified in some plants for the storage of nourishment.
A) For Food Storage, the TapRoot has been Modified.
Primary roots retain nourishment, grow fleshy, and enlarge in many cultivated plants. It is categorized as follows based on its maturity structure:-
Fusiform Root:-
1. The major root of the Fusiform type is broad in the center, tapers at both ends, and becomes spindle-shaped to store food. Radishes, for example (Raphanus Sativa).
2. Root with Conical Shape:- The primary root of the Conical type is large at the base and progressively tapers towards the apex, becoming cone-shaped to store food. Carrot, for example (Dacus Carota).
3. Root of the Napiform:- The primary root of the Napiform type is virtually spherical above and sharply tapers towards the apex to store food material. Beetroot, for example (Beta vulgaris).
B) Modified Adventitious Root For Food Storage
1. Tuberous root:- Tuberous root develops adventitious root clusters at each Runner node. Only one adventitious root among them develops irregularly bulged as a result of food storage. Sweet potato, for example (Ipomea batatus)
2. Fasciculated Root:- From the base of the stem, Fasciculated root clusters of adventitious root grow. Due to storage, all of these roots become irregularly bulged. Dahlia, for example
II.Modification of Aerial Root. Adventitious roots that emerge from the aerial sections of the shoot system provide a variety of tasks, including mechanical support, breathing assistance, food sucking, and water absorption.
a)Adventitious Root that has been adapted to provide mechanical support:-
Adventitious roots that develop from the shoot system’s aerial sections are changed to provide purposes such as mechanical support. It can be grouped into the following categories based on the type of development:-
1. Prop Root:- Adventitious roots emerge from a tree’s horizontal branches, grow downwards, reach the soil, thicken, wooden up, act as pillars, and provide mechanical support. Banyan, for example (Ficus benghalensis).
2. Stilt Root:- Stilt roots have aerial adventitious roots that sprout from the stem’s lower nodes. These obliquely extend downwards into the earth, providing additional mechanical support: Sugarcane (Saccharum officinarum)
3. Climbing Root:- Climbers have aerial adventitious roots that emerge from nodes on the stem. Plants with a weak stem). They grab the supporting object and assist with the climb. Pepper (Piper nigrum), Betel (Piper betel), and Pothas are examples.
B) Adventitious root that has been altered to provide specific physiological purposes
1. Pneumatophores:-
Plants that grow in waterlogged soil, such as swamps and marshes, have their roots immersed in saline, oxygen-depleted soil. These plants’ roots sprout unique branches that grow vertically above the soil surface and develop aeration pores known as ‘Lenticels.’ Pneumatophores, often known as ‘Breathing roots’ or ‘Respiratory roots,’ are such roots. Avecinia and Rhizophora are two examples.
2. Sucking Roots:-
For both food and shelter, some plants rely on other plants. Parasites are the name given to such plants. These plants produce ‘Haustoria,’ which are peculiar button-shaped roots that penetrate deep into the host tissue, reach the vascular bundle, and take food from there. They’re also known as’sucking roots.’ Cuscuta, Loranthus, and Viscum are some examples.
3. Epiphytic Roots:-
‘Epiphytes’ are plants that rely on other plants for protection. They never absorb food from these plants. They grow two kinds of roots: ‘clasping roots’ and ‘hanging roots.’ Clasping roots aid in keeping the plant firmly attached to the branch. The roots of hanging plants dangle freely in the air. They are made up of ‘Velamen,’ a type of spongy tissue that absorbs moisture from the air. Vanda, for example (Orchid).