Root- Introduction. Types, Anatomy, Symbiosis, Diseases


Plant roots are critical structures that anchor plants in the ground and perform a variety of important activities. They are essential in absorbing water and nutrients from the soil, providing support and stability to the plant, and storing carbohydrates reserves. Furthermore, roots promote interactions with soil microbes and contribute to nutrient cycling and ecosystem function.


Taproot System

The primary root, known as the taproot, develops straight down into the earth in plants with taproot systems. It is often thicker and longer in length than the lateral roots. Smaller lateral roots, known as secondary roots, grow out horizontally from the taproot. Dicotyledonous plants frequently have taproot systems. Carrots, radishes, and oak trees are a few examples.

Adventitious Root System

Adventitious root systems form when roots form from non-root plant components such as stems or leaves rather than the typical root initiation zone near the radicle (embryonic root). These roots can grow from any portion of the plant and conduct activities like anchoring, absorption, and reproduction. Ivy, corn, and numerous epiphytic orchids are examples of plants having adventitious roots.

Fibrous Root System

Fibrous root systems are made up of a complex web of tiny, thread-like roots that grow from the base of stem. Monocotyledonous plants like grasses, wheat, and lilies frequently have fibrous roots.

Anatomy of a root:

Root Cap: Protects the tip of the root and aids in sensing gravity.

Meristematic Zone: Contains actively dividing cells for root growth.

Zone of Cell Elongation: New cells elongate, increasing root length.

Root Meristem Anatomy

Fig: Root Meristem Anatomy

Zone of Cell Maturation/Differentiation: Cells mature and differentiate into specialized tissues.

Root Hairs: Thin projections on the epidermis that absorb water and minerals.

Apical Meristem: Region of actively dividing cells at the root tip.

Lateral Roots: Branch off from the main root, increasing water and nutrient absorption. Functions of roots in plants:

Cross Section of a Dicot Root:

  • Epidermis: Outermost layer for protection and absorption.
  • Cortex: Stores food and water, provides support.
  • Endodermis: Innermost cortex layer with the Casparian strip to regulate water flow.
  • Pericycle: Gives rise to lateral roots.
Cross Section of a Dicot Root

Fig: Cross Section of a Dicot Root

Vascular Cylinder:

  • Xylem: Transports water and minerals.
  • Phloem: Transports organic compounds.
  • Cambium (in some dicot roots): Responsible for secondary growth.

Roots in different environments:

Roots have extraordinary adaptations to various surroundings in order to enhance their ability to absorb water and nutrients. Plants generate specialized aerial roots known as pneumatophores in aquatic environments, which are provided with features such as lenticels or spongy tissues that enable gas exchange and absorb oxygen from the water. Plants in dry regions have lengthy taproots that extend deep into the soil to obtain water sources, as well as vast surface root systems that capture rainwater quickly. Epiphytic plants have spongy aerial roots that may absorb moisture from the air and droplets of water. Pneumatophores in mangroves rise above the water’s surface to promote oxygen exchange in waterlogged soils. Parasitic plants have small root systems and rely on haustoria, a specialized structure, to take nutrients from host plants.

Root symbiotic relationships:

Root symbiotic relationships are mutually beneficial relationships between plant roots and other organisms, typically microorganisms. These interactions are critical for nutrient acquisition, stress tolerance, and overall plant health. The main types include:

Mycorrhiza (Mutualistic Mycorrhizal Associations)

Mycorrhizal associations are among the most common and well-studied root symbiotic relationships that involve the interaction of plant roots with fungi known as mycorrhizal fungi. These fungi form a mutualistic partnership with plants, providing increased nutrient uptake capabilities while receiving energy-rich carbohydrates from the plant.

There are two main types of mycorrhiza:

  1. Ectomycorrhiza (ECM)

ECM involves the formation of a Hartig (complex network of root) net by fungal hyphae around the plant root, extending into the soil. This association is commonly observed in many tree species, such as pines, oaks, and birches. ECM fungi facilitate the uptake of nutrients, especially phosphorus and nitrogen, and provide protection against pathogens.

Root Colonization Structures of Ectomycorrhiza vs Arbuscular Mycorrhiza

Fig: Root Colonization Structures of Ectomycorrhiza vs Arbuscular Mycorrhiza

     b. Arbuscular Mycorrhiza (AM)

           It is characterized by the formation of arbuscules within the root cells. This association     is prevalent in the majority of plants, including most agricultural crops. AM fungi primarily enhance the uptake of phosphorus and other nutrients, improving plant growth and resilience to environmental stresses.

Rhizobia and Legumes (Nitrogen-Fixing Symbioses)

Rhizobia in nodules fix atmospheric nitrogen, providing usable nitrogen to the plant in exchange for carbohydrates. Furthermore, the bacteria reside on the plant roots in specialized structures known as nodules. They convert atmospheric nitrogen into a biologically available form (ammonium), which provides a critical nutrient to the plant. In exchange, the plant provides carbohydrates and a suitable environment for the bacteria’s growth.

Parasitic Associations

Parasitic interactions involve plants (parasites) taking nutrients from other plants (hosts) through their roots, severely effecting host growth. Examples include dodder, broomrape, and witchweed (root parasites) and mistletoe and Indian paintbrush (hemiparasites). Managing parasitic plants is vital for agriculture, with management strategies such as physical removal and chemical treatments employed to limit their effects.

Root diseases:

The term “root diseases” refers to a variety of diseases and conditions that have an impact on a plant’s roots and can cause injury, yellowing or wilting of leaves, death, stunted growth, discoloration of root, or decreased root function. Because the roots are so important for absorbing water and nutrients, securing the plant in the soil, and supporting above-ground growth, these diseases can be damaging to the general well-being and productivity of plants.

Pathogens (such fungi, bacteria, or viruses), environmental circumstances, habits of cultivation, and problems with the soil are the causes of root illnesses. Direct root infection by pathogens can result in root rot, rotting, or the development of toxins that harm the roots. Root infections can flourish in environments with inadequate soil drainage, excessive watering, or severe pH levels. Root infections can also arise as a result of cultural activities such as poor planting methods, ongoing monoculture, or physical harm to roots.

Identifying this condition early is crucial for managing stands. Maintaining a healthy soil, using suitable planting techniques, establishing crop rotation, controlling irrigation and drainage efficiently, and providing a balanced nutrient supply are all necessary to prevent root infections.

Discoloration of root. Root Disease

The major root diseases are:

  • Brown root disease: Phellinus noxius (Fomes noxius)
  • White root disease: Rigidoporus lignosus (Fomes lignosus)
  • Black root disease: Rosellinia pepo Pat.
  • Collar crack: Armillaria mellea Vahl.


van Ooij, C. Establishing the roots of a relationship. Nat Rev Microbiol 9, 629 (2011).

Ryan, P.R., Delhaize, E., Watt, M. and Richardson, A.E., 2016. Plant roots: understanding structure and function in an ocean of complexity. Annals of Botany, 118(4), pp.555-559.

Leave a Comment

Your email address will not be published. Required fields are marked *