A dicotyledonous root plays a crucial role in plant growth by anchoring the plant absorbing water and transporting nutrients. When viewed under a microscope in a transverse section (T.S.) the internal structure reveals several distinct layers each with specialized functions.
In this topic we will explore the anatomy of a transverse section of a dicot root discussing the structure function and importance of each tissue layer.
Overview of Dicotyledonous Root Structure
A dicotyledonous (dicot) root exhibits a well-organized vascular system arranged in a radial pattern. The xylem and phloem are located in separate bundles forming a characteristic star-shaped pattern. The main tissues observed in a transverse section include:
- Epidermis
- Cortex
- Endodermis
- Pericycle
- Vascular Bundle (Xylem and Phloem)
- Pith (if present in some dicots)
Each of these layers plays an essential role in the plant’s overall health and development.
Detailed Anatomy of a Transverse Section of a Dicot Root
1. Epidermis: The Protective Outer Layer
The epidermis is the outermost layer of the root responsible for protection and absorption.
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Structure:
- Composed of a single layer of thin-walled cells.
- Lacks a cuticle to facilitate water absorption.
- Contains root hairs which increase the surface area for absorption.
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Function:
- Protects the root from pathogens.
- Absorbs water and minerals from the soil.
2. Cortex: The Storage Region
The cortex lies beneath the epidermis and consists of parenchyma cells with intercellular spaces.
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Structure:
- Made up of loosely packed cells that allow air circulation.
- Often stores starch and nutrients.
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Function:
- Stores food and nutrients.
- Facilitates the transport of water and minerals to the vascular bundle.
3. Endodermis: The Selective Barrier
The endodermis is a single layer of tightly packed cells that regulates the entry of water and minerals into the vascular tissue.
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Structure:
- Contains a specialized structure called the Casparian strip made of suberin (a waterproof material).
- Surrounds the vascular bundle.
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Function:
- Controls the movement of water and nutrients into the vascular tissue.
- Prevents the backflow of absorbed substances.
4. Pericycle: The Origin of Lateral Roots
The pericycle is a thin layer of meristematic cells located just beneath the endodermis.
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Structure:
- Made up of a few layers of compact cells.
- Has the ability to divide and form new cells.
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Function:
- Gives rise to lateral roots.
- Plays a role in secondary growth in woody dicots.
5. Vascular Tissue: Xylem and Phloem
The vascular bundle in a dicot root consists of xylem and phloem which are arranged in a radial pattern.
Xylem: Water-Conducting Tissue
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Structure:
- Arranged in an X-shaped or star-shaped pattern.
- Composed of vessels tracheids xylem parenchyma and fibers.
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Function:
- Conducts water and minerals from the roots to the rest of the plant.
- Provides structural support.
Phloem: Food-Conducting Tissue
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Structure:
- Located between the arms of the xylem.
- Composed of sieve tubes companion cells phloem parenchyma and fibers.
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Function:
- Transports sugars and nutrients from the leaves to the root.
6. Pith: The Central Storage Tissue (Sometimes Absent in Dicots)
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Structure:
- Made of parenchyma cells.
- May be reduced or absent in dicot roots.
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Function:
- Stores nutrients.
- Provides additional structural support.
Comparison: Dicot Root vs. Monocot Root
| Feature | Dicot Root | Monocot Root |
|---|---|---|
| Xylem Arrangement | Star or X-shaped pattern | Ring-like pattern |
| Pith | Usually absent or small | Prominent and well-developed |
| Cortex | Narrow | Wide |
| Secondary Growth | Present in woody plants | Absent |
Functions of a Dicotyledonous Root
- Anchorage: Helps the plant remain stable in the soil.
- Absorption: Uptakes water and minerals for growth.
- Conduction: Transports nutrients and water to other parts of the plant.
- Storage: Some roots store food such as in carrots and beets.
- Hormone Production: Produces growth hormones like cytokinins.
Importance of Studying the Transverse Section of a Dicot Root
Understanding the transverse section of a dicot root is crucial for:
- Botany and Plant Science: Helps in identifying plant species.
- Agriculture: Aids in improving crop growth and soil health.
- Horticulture: Assists in developing better irrigation and fertilization techniques.
- Plant Pathology: Helps in diagnosing root diseases and deficiencies.
A transverse section of a dicotyledonous root reveals an intricate network of tissues that work together to support plant growth. Each layer from the epidermis to the vascular bundle plays a crucial role in water absorption nutrient transportation and structural support.
By understanding the anatomy and function of dicot roots we can enhance agricultural practices improve plant health and ensure better crop productivity.
