Parenchyma in plants are the types of simple permanent tissue which has some of the ideal properties that distinguish it from the other cells:
Cell division: Parenchyma tissue has not the ability to undergo cell division.
Vacuole: These comprises a large vacuole.
Nature: Structurally and physically, parenchyma is a kind of unspecialized tissue.
Modification: Parenchyma modifies itself to perform diverse functions in a plant cell.
When the parenchymatous cells appear in aggregates, they carry a polygonal shape by having 14-sided polyhedral cells. Parenchyma cells also appear in certain other forms like spherical, elongated, stellate etc.
Content: Parenchyma in Plants
Definition of Parenchyma tissue
It can define as the simple permanent tissue, which is usually thin-walled and functions as a “ground tissue” by forming a packaging material of all the non-woody structures like leaves, roots and stems. Term parenchyma has originated from the Greek term “Para” which means beside and “Enchyma” which means inclusion. It is supposed to be introduced during the 17th century when Robert Hooke discovered the plant cells.
Parenchyma tissue is a type of non-vascular tissue that is composed of simple, living and undifferentiated cells. A parenchymatous tissue modifies into three major types, namely chlorenchyma, aerenchyma and prosenchyma.
Types of Parenchymatous Tissue
Parenchyma tissue in plants can be classified based on their shape, arrangement and functions.
Based on Functions
Based on the functions of parenchymatous tissue, there are four major kinds:
Chlorenchyma: It can define as the parenchymatous cell that possesses chloroplast. Thus, it assimilates the chlorophyll pigment and refers as “Assimilatory parenchyma”. In leaves, it differentiates into mesophyll cell that possesses two distinct, palisade and spongy parenchymatous cell. It is present in the mesophyll zone of the leaves, sepals and phyllodes.
Function: Participates in photosynthesis.
Aerenchyma: It can define as the parenchymatous cell that comprises of large air-filled intercellular spaces and commonly refers to “Air storing parenchyma”. Aerenchyma cells are most widely present in the roots, stems and leaves of hydrophytes. It comprises few large-sized air cavities between the parenchymatous cells to perform various functions.
Function: Participates in gaseous exchange and maintains the buoyancy of hydrophytes.
Prosenchyma: It can define as the parenchymatous tissue that possesses elongated cells with a thickened wall. The prosenchyma appears spindle in shape with tapering ends.
Function: Promotes rigidity to a plant.
Storage parenchyma: It can define as the parenchymatous tissue that is composed of large-sized vacuolated cells that stores water, minerals, sugar, protein granules, oil droplets etc. The cell-wall of storage parenchyma is generally thick because of hemicellulose deposition.
Function: Helps in the storage of food.
Besides this, there are few other kinds of parenchyma cells like:
Xylem parenchyma: This kind of parenchymatous cells possess small-sized cell and encloses by a thickened cell wall.
Function: Facilitates water and mineral conduction.
Phloem parenchyma: This kind of parenchymatous cells possess elongated cells and encloses by a thin cell wall.
Function: Facilitates conduction of food prepared by the leaves.
Epidermis parenchyma: This kind of parenchymatous cells are elongated with zero intercellular space. Epidermis parenchyma possesses a cutinized cell wall or cuticle enclosing a single-layered epidermis.
Function: Protects the plant in counter to environmental stress.
Based on Shape and Arrangement
There are two types of parenchymatous tissue based on the shape and arrangement:
Oval or loose parenchyma: Here the parenchymatous cells are irregular, oval in shape and having loose arrangement with more intercellular space. This kind of parenchyma is present in the inner cortex of stem.
Angular or intact parenchyma: Here, the parenchymatous cells are polygonal in shape and having intact cells with small or no intercellular space. This kind of parenchyma is present in the outer cortex of root.
Characteristics of Parenchyma in plants
A parenchymatous cell shares many features based on cell morphology and physiology.
- Shape: The shape is generally polygonal when they lie close to each other and sometimes possess oval or spherical shape.
- Symmetry: Possesses an isodiametric symmetry.
- Cell-wall: The cell-wall of parenchyma is usually thin and formed primarily of cellulose.
- Nature: It behaves like a living cell.
- Occurrence: Predominates in the smoother parts of leaves, stems and roots.
- Constitution: Parenchyma tissue is the most usual and abundant tissue that constitutes most of the plant’s part.
- Vacuoles: A parenchyma cell comprises a large-sized vacuole that is located centrally.
- Functions: Parenchyma cell performs a functional role in food storage and plant’s protection.
Distribution: Parenchyma tissue is distributed in the following parts of a plant:
- Pith and cortex region of stem and root.
- Mesophyll of leaves
- The flesh of succulent roots
- The endosperm of seeds etc.
Arrangement: When the parenchyma cells attain maturity, they become firmly intact with each other without any intercellular space.
Example: Endosperm tissue of seeds
Some parenchyma cells comprise a more intercellular space by the loose arrangement of the neighbouring cells.
Example: Stems and leaves of hydrophilic plants.
Structure of Parenchyma Tissue
A structure of parenchyma tissue includes:
- Aggregates of numerous polygonal or spherical parenchyma cells with a living protoplast.
- A large central vacuole.
- Peripheral cytoplasm incorporated with a nucleus, which can be one or sometimes more in number.
It is the most abundant and common tissue of the plant where the cells can have a compact or loose arrangement with little, large or no intercellular space. A parenchyma cell may also contain tannins or some resinous materials. Plasmodesmata join the cells of parenchyma tissue. The cell sap of parenchyma generally stores food source like carbohydrates, fats, oils droplets, protein granules etc.
Functions of Parenchyma in plants
It includes the following tasks:
- Chlorenchyma participates in the photosynthetic activity of a plant, by having chloroplastids.
- Aerenchyma functions to provide air spaces that facilitate gaseous exchange and provide buoyancy to the macrophytes for floating.
- The mechanical strength of a plant is promoted by the elongated cells of prosenchyma.
- Storage parenchyma functions to store or reserve various food materials.
- Xylem parenchyma facilitates conduction of water and minerals unidirectionally from roots to the different parts of the plant.
- Phloem parenchyma facilitates lateral food conduction from the leaves to roots.
- Epidermal parenchyma protects the plant and minimizes transpiration.
Therefore, we can conclude that parenchyma tissue modifies to perform diverse functions in a plant body.