Parenchyma Cells

Parenchyma is a simple permanent tissue found in plants. It forms a large part of the ground tissues. Parenchyma forms a major part of the ground tissues and is also present in vascular tissues (xylem and phloem). Parenchyma cells are living and simple in structure. They are non-vascular, and they do not transport water like xylem or phloem. These cells are undifferentiated but can change to perform many functions.

Parenchyma cells are important because they can divide even after maturing. This helps plants heal wounds and grow new tissues. Parenchyma cells are totipotent; a single parenchyma-derived cell (like a zygote) can regenerate into a whole plant.

Parenchyma cells form continuous masses in plants. They can be found in the pith and cortex of stems and roots. They are also in the mesophyll of leaves, fruit flesh, and seed endosperm. Sometimes, parenchyma cells join with other cells to form complex tissues. For example, xylem and phloem have parenchyma cells as part of them.

These cells help in photosynthesis, storage, secretion, and respiration. They also assist in radial transport of water and solutes inside plants.

Structure of Parenchyma Cells

Parenchyma cells are living and have a nucleus and a protoplast.
They are usually polygonal, oval, round, or elongated in shape.
The cells can be closely packed or have small spaces called intercellular spaces.
Their cell walls are thin and made of cellulose and hemicellulose.
Plasmodesmata are small channels that connect parenchyma cells for communication.
They contain many small vacuoles. They merge into a large central vacuole.
Vacuoles store water, helping plants keep their shape and strength.
Some parenchyma may have slightly thickened walls (e.g., prosenchyma) for extra support, but they differ from sclerenchyma.
Chloroplasts are present in parenchyma cells that perform photosynthesis.

Types of Parenchyma Cells

Parenchyma cells vary by function and location in plants. Their types include:

Chlorenchyma

They have chloroplasts and carry out photosynthesis.
They are found in leaf mesophyll and other green parts like stems.

Transfer Cells

They help move solutes over short distances.
The walls of these cells grow inward, increasing their surface area.
Transfer cells are found in areas like nectaries and salt glands.

Vascular Parenchyma

These cells are part of vascular tissues and are of two types:

Phloem Parenchyma

They are elongated cells with dense cytoplasm.
They store food and substances like resins and latex.
They are absent in monocot plants.

Xylem Parenchyma

They are thin-walled cells near xylem vessels.
They store starch, fats, tannins, and crystals.
They help move water radially and protect vessels during drought.

Storage Parenchyma

These cells store food materials like starch, proteins, and water.
They are found in potato tubers, seeds, and succulent plants like cacti.
They also provide moisture for new shoot growth underground.

Prosenchyma

Fibre-like cells that are thick-walled and provide strength to plants.

Aerenchyma

These cells have large air spaces for gas exchange.
Common in aquatic plants like rice, helping in buoyancy and oxygen supply.
Aerenchyma connects roots and shoots for air diffusion.

Epidermis Parenchyma

Found in leaves of some gymnosperms with a cutinized wall.
Helps reduce water loss and protects the plant surface.

Conjunctive Parenchyma

It is present in the stele of roots (especially in monocots) and helps link vascular bundles.
It absorbs water and minerals from the soil.

Functions of Parenchyma Cells

Parenchyma cells have many important functions in plants:

Storage

They store starch, water, oils, and other substances. Potato tubers and cassava have large starch storage in the parenchyma.

Transport

They help transport nutrients and chemicals within the plant. Xylem parenchyma aids in radial water movement.

Photosynthesis

Chlorenchyma cells perform photosynthesis in green plant parts.

Gas Exchange

Aerenchyma cells allow gases like oxygen to move inside plants.

Protection

Some parenchyma cells may store defensive compounds (tannins, crystals) to deter herbivores.

Totipotency

Parenchyma cells can change into other cell types when needed.

Buoyancy

Air spaces of aerenchyma help aquatic plants float.

Mechanical Strength

Water-filled parenchyma cells provide turgor pressure, giving strength. Thick-walled cells also add rigidity to the plant.

Healing and Regeneration

Parenchyma cells divide to heal wounds and repair damage. Tyloses in xylem parenchyma prevent vascular damage during drought.

Summary

Parenchyma cells are vital for storing nutrients and water in plants. They assist with photosynthesis and gas exchange in plant tissues. They are found in areas like the pith and mesophyll; these cells can divide and heal. They also help plants with mechanical strength and transport water efficiently.

FAQs

Q1. Where are parenchyma cells found?

A. Parenchyma cells are found in the pith, cortex, and mesophyll of leaves. They are also found in fruit flesh and the seed endosperm of plants.

Q2. What is the function of parenchyma cells?

A. Parenchyma cells store food, water, and nutrients. They also assist in photosynthesis and gas exchange. They help in the healing and regeneration of plant tissues.

Q3. What are chlorenchyma cells?

A. Chlorenchyma cells are plant cells that contain chloroplasts and are responsible for photosynthesis.