The root is the underground part of a plant. Root develops from the radicle of the germinated seed.
Important functions of the roots :
- Absorption of water and minerals.
- In anchoring the plant in the soil
Important Characteristic of roots :
- The roots in the plants lack node.
- They are positively geotropic, negatively phototropic and positively hydrotropic.
Regions of root:
There are four zones in the root, Root cap zone, Meristematic zone, Zone of elongation, and zone of maturation.
Root cap zone – Root cap is a smooth protective structure in the root cap zone.
Generally, there is one root cap in the plant but Pandanus has multiple toot caps and Eichhornia, Lemna, and Pistia have not root caps (instead of root cap they have root pockets).
Meristematic zone – This zone is also known as the zone of cell division as the cells are actively performing cell division. The cells of this zone are thinly walled with no intercellular spaces.
Zone of elongation – They are situated just behind the meristematic zone. The cells of this region don’t have the power of division. This region is responsible for the absorption of water and minerals from the soil.
Zone of maturation – This region contains root hairs which increase the surface area of roots for absorption of minerals salts and water.
Type of root system:
Taproot system and Adventitious root system are two main type of root system present in plants.
In the taproot system, the primary or tap root develops from radical of the germinating seeds.
In the adventitious root system, the toots produced from any other part of the plant except the radical.
Modification of taproot
The important modifications of taproot are Fleshy tap root, Nodulated taproot, and Respiratory roots.
They store food. They can be conical, fusiform, napiform, and tuberous taproot.
- Conical taproots are conical in shape. e.g. Carrot (Dacucus carota).
- Fusiform taproots are broader in the middle and narrower at both ends.
- Napiform tap roots swell extraordinarily in the middle and become abruptly narrower towards the apical region. e.g. Brassica rapa ( shalzum).
- Tuberous taproots are thick and fleshy tubers with an irregular shape. e.g. roots of Mirabilis jalapa.
These typed of roots are a characteristic feature of Leguminosae family. They are also called tuberculated roots or nodulated roots. These nodes contain nitrogen-fixing bacteria, which help in nitrogen fixation. e.g. Rhizobium.
These roots are found in the plants which grow mainly in the marshy areas. The roots are negatively geotropic, the underground root of the plant start growing up and become aerial.
These roots have minute pores on the tips called pneumathodes. These pneumathodes help in exchange of gases so, these are also called as Respiratory roots or pneumatophores. e.g. Rhizophora.
Modification of Adventitious root
The adventitious root gets modified to perform a specific function like storage of food, Mechanical support, physiological functions.
Adventitious root modification for storage of food
The adventitious root gets swollen and becomes thick due to storage of food.
In considering the place of swelling and the shape of the root, it can be Tuberous root, Fasciculated root, Moniliform root, Annulated root, Palmate root, and Nodulose roots.
- Tuberous roots arise from internode of stem and do not have a definite shape. e.g. Sweet potato (Ipomoea batata).
- Fasciculated roots produced from the lower node of stem and form a cluster.e.g. Dahlia.
- Moniliform roots are swollen at regular intervals and give a bead like an appearance as seen in the necklace.
- Nodulose roots are swollen at their tips. e.g. Curcuma amada (mango ginger).
Adventitious root modification for Mechanical support
For providing mechanical support to the roots modified into buttress roots, slits roots or Brace roots, Prop or Pillar roots, Contractile roots and Climbing or Clinging roots.
- Buttress roots arise from the base of the tree.e.g Bombax.
- Stilt or Brace roots develop from the basal nodes of the stem near the soil.e.g. Saccharum officinarum (Sugarcane), Zea mays (maize), and Pandanus tincotorius.
- Prop or Pillar roots develop from large horizontal aerial branches. They grow vertically downwards, reach to the soil and finally become thick. so, the give a pillar-like appearance. e.g. Banyan tree.
- Climbing or Clinging roots arise from the nodes and help the plant in climbing. e.g Ficus pumila.
Adventitious root modification for Physiological functions
Some roots modified in Photosynthetic roots, Haustorial roots, epiphytic roots, Reproductive roots, and floating roots to perform physiological functions.
- Assimilatory or Photosynthetic roots develop chlorophyll and become green. These roots carry photosynthesis.e.g. Trapa, Tinospora.
- The Parasitic or Haustorial roots are present in the parasitic plants. They penetrate the plant and absorbs nourishment from the host tissues. e.g. Cuscuta, a parasite of the plants like Duranta, Acacia.
- Epiphytic roots hang in the air and absorb hygroscopic water by special Velamen tissue. e.g. Vanda.
- Floating roots arise from nodes and store air, become inflated and spongy. e.g. Jussiaea.