Like any multicellular organism, a plant is characterized by cell differentiation, the specialization of cells in structure and function. Cell differentiation may involve changes both in the cytoplasm and its organelles and in the cell wall. And the structural adaptations in the different cells make their specific functions possible.
Parenchyma cells are the biochemistry machines of the plant. They are usually depicted as the typical plant cell because they are not very specialized. Parenchyma cells are thin-walled cells that make up the inside of many non-woody plant structures (soft parts) including stems, roots, and leaves. These cells synthesize (by photosynthesis) and store organic products in the plant. Most of the plant’s metabolism takes place in these cells. They are alive at maturity and forms the basis for all plant structure and function.
Generally parenchyma cells are involved in storage of starch, sucrose, protein, water, phenol derivatives, many mineral substances, etc. These cells are also active in other metabolisms like respiration, protein synthesis. The thin, permeable primary walls of parenchyma cells enables the transport of small molecules between them, and their cytoplasm is responsible for a wide range of biochemical functions such as nectar secretion, or the manufacture of secondary products that discourage herbivory. Parenchyma cells retain the ability to divide throughout their lives, so they are also important in vegetative regeneration and wound healing.
Parenchyma cells compose the middle layer of leaves as well as the outer and inner layers of stems and roots. The soft tissue of fruits is also composed of parenchyma cells. They are usually loosely arranged with prominent intercellular spaces.
Types of Parenchyma cells
- Chlorenchyma is the parenchyma in which the cells contain large number of chloroplasts. Chlorenchyma takes part in photosynthesis. It occurs in the leaves and other green parts of the plant body.
- Prosenchyma is a type of parenchyma where cells are elongated with tapering ends, serve as a supporting tissue.
- Aerenchyma is the parenchyma in which the cells enclose large intercellular spaces that are filled with air. Aerenchyma helps in buoyancy and respiration. It is characteristically found in aquatic floating plants.
- Vascular parenchyma is the parenchyma, which is found associated with the vascular tissues xylem and phloem. Accordingly, it is distinguished into xylem parenchyma and phloem parenchyma.
- Medullary parenchyma is the parenchyma, which is found radially arranged in between the vascular bundles in the stem. It is meant for storage of reserve food.
- Conjunctive parenchyma is the parenchyma, which occurs in the root system. It is specially meant for storage of water.
- Armed parenchyma is the parenchyma, which is found in the epidermis of leaves in some gymnosperms. The cells have many spiny projections. It is defensive in function.