Permanent tissue : Characteristics, types and function

Permanent tissues are mature plant cells that have lost the ability to divide. They develop from meristematic tissues and specialize in specific functions like support, storage, or transport. These tissues can be simple (made of one cell type, e.g., parenchyma) or complex (multiple cell types, e.g., xylem and phloem). Once formed, they remain in their role permanently to maintain plant structure and function.

Summary of Permanent tissue

• Permanent tissue is a group of mature plant cells that have lost the ability to divide and are specialized for specific functions.
• It is mainly of two types: simple permanent tissue (like parenchyma, collenchyma, and sclerenchyma) and complex permanent tissue (like xylem and phloem).
• They help the plant with important tasks like support, storage, photosynthesis, and the transport of water, minerals, and food.

Characteristics of Permanent tissue

1. Non-Dividing Cells: These tissues consist of mature cells that have lost the ability to divide.
2. Specialized Functions: They perform specific roles like support (collenchyma, sclerenchyma), storage (parenchyma), or transport (xylem, phloem).
3. Fixed Shape & Size: Cells are fully developed with a permanent structure.
4. Large Vacuoles: Often contain a central vacuole for storage and maintenance of turgidity.
5. Thick Cell Walls: In some types (e.g., sclerenchyma), cells have thick, lignified walls for strength.
6. Dead or Living Cells: May include dead cells (e.g., sclerenchyma fibers) or living cells (e.g., parenchyma).
7. Derived from Meristem: Formed after differentiation of meristematic tissues.

Types of Permanent tissue

Permanent tissues are plant tissues made up of mature cells that have lost the ability to divide. These tissues help the plant in support, storage, protection, and transport of water and nutrients. Based on their structure and function, permanent tissues are divided into two main types:

1. Simple Permanent Tissue

Simple permanent tissues are made up of only one type of similar cells. All the cells in this tissue look alike and perform similar functions. They are mainly responsible for basic functions like support, storage, and photosynthesis. Simple tissues are of three types:

A. Parenchyma

Parenchyma is the most basic and widely distributed type of simple permanent tissue. The cells are living, with thin cell walls made of cellulose, and usually have a large central vacuole. These cells are loosely packed with intercellular spaces between them, allowing easy exchange of gases and nutrients.

Functions of Parenchyma:

• Storage: Parenchyma stores food, water, starch, oils, and waste materials in various plant parts like roots, fruits, and tubers.
• Photosynthesis: In green parts like leaves, parenchyma contains chloroplasts and is known as chlorenchyma, which helps in photosynthesis.
• Buoyancy: In aquatic plants, a type of parenchyma called aerenchyma contains large air spaces, making the plant light and buoyant.
• Healing and Regeneration: Parenchyma helps in the healing of plant wounds and regeneration of tissues.

2. Collenchyma

Collenchyma is a type of simple permanent tissue that provides mechanical support and flexibility to the plant. These cells are living and have unevenly thickened cell walls, especially at the corners due to the presence of pectin and cellulose. Collenchyma cells are elongated and closely packed with little or no intercellular space.

Functions of Collenchyma:

• Support: It gives support to growing stems, petioles, and leaves without restricting growth.
• Flexibility: The flexibility provided by collenchyma allows the plant to bend without breaking, especially in windy conditions.
• Growth: Found in actively growing parts of the plant, collenchyma cells can also stretch as the plant grows, providing dynamic support.

3. Sclerenchyma

Sclerenchyma is a simple permanent tissue made up of dead cells with very thick, lignified cell walls. The cells are long, narrow, and have no internal protoplasm. Because of their thick walls, sclerenchyma cells are extremely rigid and strong, giving hardness to parts of the plant.

Functions of Sclerenchyma:

• Mechanical Strength: Sclerenchyma provides strong support to the plant and helps it remain upright.
• Protection: It forms hard protective coverings, such as the seed coat and the shells of nuts.
• Tissue Hardening: Due to the presence of lignin, sclerenchyma contributes to the hardness of plant tissues, especially in mature regions like stems and barks.

Types of Sclerenchyma:

• Fibers: Long, slender cells found in stems, leaves, and vascular tissues.
• Sclereids: Shorter, irregular cells that provide toughness, found in seed coats, nutshells, and gritty fruits like pears.

2. Complex Permanent Tissue

Complex permanent tissues are made of different types of cells working together to perform specialized functions, mainly transport of substances within the plant. There are two main types:

A. Xylem

Xylem is a complex permanent tissue responsible for the transport of water and minerals from the roots to all parts of the plant. It mainly consists of dead cells, which are joined together to form long, continuous tubes. Xylem not only helps in conduction but also provides mechanical support to the plant due to its thick, lignified cell walls.

Main Components of Xylem:

• Tracheids: Long, tube-like dead cells with tapering ends that conduct water and also give support.
• Vessels: Wider and shorter than tracheids; form long tubes for efficient water conduction in flowering plants.
• Xylem Fibers: Dead and thick-walled cells that provide additional strength.
• Xylem Parenchyma: The only living cells in xylem; they store food and help in the sideways movement of water.

Functions of Xylem:

• Conducts water and minerals from roots to stems and leaves.
• Provides structural strength to the plant.
• Helps in the upward movement of water through a process called transpiration pull.

B. Phloem

Phloem is a complex permanent tissue responsible for the transport of food, especially sugar produced during photosynthesis, from leaves to other parts of the plant. This process is called translocation. Unlike xylem, most of the phloem cells are living.

Main Components of Phloem:

• Sieve Tubes: Long, tube-like cells with pores; they carry food throughout the plant.
• Companion Cells: Located beside sieve tubes; help them function by managing their metabolism.
• Phloem Fibers: Only dead cells in phloem; provide mechanical support.
• Phloem Parenchyma: Stores food and helps in lateral transport.

Functions of Phloem:

• Transports prepared food from leaves to growing and storage parts of the plant.
• Helps in distributing nutrients for growth and development.
• Supports tissues through phloem fibers.

Functions of Permanent tissue

Permanent tissues are the tissues in plants that have fully grown and matured. Unlike meristematic tissues, they do not divide anymore. Instead, they perform important and specific functions that help the plant live, grow, and stay strong. Below are the main functions of permanent tissues:

1. Support and Strength

Many permanent tissues provide mechanical support to the plant. For example, collenchyma offers flexible support to growing stems and leaves, while sclerenchyma, with its thick and lignified walls, gives hard, rigid support to older plant parts like stems and seed coats. This helps the plant remain upright and face harsh weather like wind or rain.

2. Storage of Food and Water

Parenchyma cells play a major role in storing food, water, starch, oils, and other substances. These storage tissues are found in roots, stems, fruits, and tubers. This stored food helps the plant grow and survive during unfavorable conditions.

3. Transport of Water and Minerals

Xylem, a complex permanent tissue, is responsible for transporting water and minerals from the roots to the leaves and other parts of the plant. It forms a system of tubes made up of dead cells like tracheids and vessels. This upward movement of water is essential for photosynthesis and overall plant health.

4. Transport of Food

Phloem is another complex permanent tissue that transports food made in the leaves (through photosynthesis) to other parts of the plant, including growing regions and storage organs. This process is called translocation and ensures that all parts of the plant receive the nutrients they need to survive and grow.

5. Photosynthesis

Some parenchyma cells contain chloroplasts and are known as chlorenchyma. These cells are found mainly in leaves and help in performing photosynthesis, which is the process by which plants make their food using sunlight, water, and carbon dioxide.

6. Healing and Regeneration

Parenchyma cells are also involved in repairing damaged tissues. When a plant is injured, these cells can help in healing wounds and regenerating tissues, especially in areas where the plant is still growing.

7. Buoyancy in Aquatic Plants

In water plants, a type of parenchyma called aerenchyma helps the plant float. These cells have large air spaces that make the plant lighter and allow it to stay on the surface of the water, which helps in gas exchange and photosynthesis.

Conclusion

Permanent tissues in plants are made up of mature cells that have stopped dividing. These tissues develop from meristematic tissue and are specialized to perform specific roles. Based on their structure, permanent tissues are of two main types: simple and complex. Simple permanent tissues include parenchyma, collenchyma, and sclerenchyma, which mainly help in support, storage, and protection.

Complex permanent tissues like xylem and phloem are made of different cell types and are responsible for transporting water, minerals, and food throughout the plant. Permanent tissues also help the plant stand strong, store food and water, carry out photosynthesis, and even heal wounds. Though they don’t divide like growing tissues, they play a vital role in keeping the plant healthy and functioning properly.

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