Parenchyma is a simple permanent tissue that makes up large portions of various plant organs. It consists of thin-walled living parenchymatous cells.
The word parenchyma comes from the Greek words para and enchyma. Para means besides, and enchyma means infusion (i.e., tissue).
Parenchyma is called the fundamental tissue of the plant as it forms the ground tissue.
Definition of Parenchyma Cells
Parenchyma cells are simple, thin-walled, isodiametric living cells that make up the bulk of plant tissues, providing support and storing food materials.
Distribution
- Parenchyma cells are found in large portions of all plant organs.
- They are distributed in the pith, cortex of the root, stem, mesophyll of the leaf, fleshy part of the fruit, and endosperm of the seed.
- These cells may also occur in conducting tissues like xylem and phloem (e.g., xylem parenchyma, phloem parenchyma).
Structure of Parenchyma Cells
- Cells are usually isodiametric, but they may be spherical, oval, or polygonal.
- Intercellular spaces are present between the cells, but these spaces are usually very small. Hence, cells are closely packed.
- The cell wall is thin and composed of cellulose and hemicellulose.
- Each cell contains dense living protoplast with a prominent nucleus.
- It also contains one or many vacuoles.
- Many cell organelles are found in the cytoplasm, such as the chloroplasts, ribosomes, endoplasmic reticulum, etc.
- A few parenchyma cells (e.g., cotyledons of many leguminous plants) contain starch and protein.
Types of Parenchyma Cells
Based on their functions, parenchyma cells are of the following types:
1. Chlorenchyma
- Parenchyma cells that contain chloroplasts are called chlorenchyma.
- These cells are usually found in the mesophyll of leaves and the outer cortex of young stems.
- Cells are loosely arranged with numerous intercellular spaces.
- Chlorenchyma helps in photosynthesis.
2. Aerenchyma
- Parenchyma cells with well-developed and large intercellular spaces are called aerenchyma.
- It is present in many aquatic plants.
- Aerenchyma gives buoyancy to the aquatic plants.
3. Prosenchyma
- In this type, the parenchyma cells are elongated, thick-walled, and tapper at both ends.
- They are present in the pericycle of some vascular plants.
- Lack of intercellular spaces between the cells.
- Prosenchyma mainly provides mechanical strength to plants.
4. Xylem Parenchyma
- These cells are associated with xylem tissue.
- Each cell is thin-walled and elongated.
- Xylem parenchyma helps in the conduction of water and minerals.
5. Phloem Parenchyma
- These parenchyma cells are associated with phloem tissue.
- Like xylem parenchyma, each phloem parenchyma cell is also thin-walled and elongated.
- It helps in the transport of food.
6. Idioblast
- These are specialised parenchyma cells.
- Idioblast can produces and stores tannins, oils, and calcium oxalate crystals.
Functions of Parenchyma Cells
- Parenchyma cells mainly function for the storage of food materials.
- They form the ground tissue of plants.
- Some parenchyma cells have the power of cell division (i.e., meristematic in nature). They play an important role in the healing of wounds.
- Chlorenchyma contains chloroplasts and can take part in photosynthesis.
- Aerenchyma cells in aquatic plants maintain buoyancy and help in gaseous exchange.
- Many metabolic activities take place in living parenchyma cells.
- Prosenchyma cells give mechanical support to the plant.
- Both xylem and phloem parenchyma play an important role in the movement of water and solutes.
- Parenchyma cells in the epidermis of the root, stem, and leaf have cutinized peripheral walls, which protect the inner tissues.
- They can store waste materials and ergastic substances.
- Some parenchyma cells are involved in the secretion of many biochemical substances such as nectar, resin, and oils.
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