When the similar cells get aggregate to form the organized structure to carry out the specific function is known as tissue. Likewise the animal tissues, plant tissues also consist of numerous multicellular cells. A tissue is the collection of the functionally and morphologically similar cells and their core materials.
Plant tissue provides the mechanical strength to the plant and has many dead cells also. It also gives flexibility and elasticity to the plants and its organs. The plant tissues functions in bending and stretching of the plants, it regulates in the transportation of water, nutrients and other materials.
With the continuous division of cells, the new cells are produced and result in the growth of the plants. Importantly, tissues also function in photosynthesis. respiration, metabolism, regeneration, etc.
On the basis of the capability of the plant cell to divide; there are two categories under which plant tissue falls: meristematic tissue and permanent (non-meristematic) tissue.
These are small, cuboidal and tightly packed cells that keep on growing and thus forming new cells. Such cells have the potential to divide and redivide. Such cells are present in the growing part of the plant, that helps in differentiating, enlarging and expanding of the different types of tissues and thus benefits the plant in growth. The cells of the meristematic tissues lack vacuoles as vacuoles prevent quick cell division and give rigidity to the cell.
On the basis of regions of growth of the plants, meristematic tissues are of three types: Apical meristems, lateral meristems, and intercalary meristems.
- Apical Meristems is found on the tips of growing roots and stems, and thus increasing their length and ultimately upsurging the growth of the plant.
- Lateral Meristems is found on the sides of the roots and stems, and thus increasing their width or thickness, thus supporting the growth of the plant.
- Intercalary or Axillary Meristems are present at the base or internodes of the leaves. It helps in the development of the leaves, nodes and other organs of the plants.
Permanent tissues originate from the old meristematic cells when these (old meristematic cells) lose the potential to divide and expand, they turned into the permanent one.
Permanent tissues are also known as the matured meristematic tissues. So, such cells have the defined size and shape and perform the specific functions. Such cells can be dead or living. These cells undergo the process of cellular differentiation where they (cells) forms the permanent size, shape and ready to perform a specific function.
Such tissues differentiate into two different types of tissues, which are simple permanent tissues, and complex permanent tissues.
Simple Permanent Tissues are further divided into collenchyma, sclerenchyma, and parenchyma on the ground of their functions.
The cells have thick walls and provide mechanical support to the plants. These tissues are usually present in young plants and thickened part of the cell wall of such cells is always be there in new growing parts of the plants.
The cells are living, irregularly thick, and elongated that is made up of pectin or cellulose with no or less intercellular spaces. These cells play main role in providing mechanical strength as well as elasticity to the aerial and new growing part of the plant.
These cells also have a thick and longwall due to the presence of lignin. These cells are dead and do not have the nucleus, cytoplasm as well as intercellular spaces.
These cells are present in the veins of the leaves, stems and near vascular bundles. Such cells provide strength and rigidity and also make the plant hard to bear external shock and stress.
These cells are abundantly present in plants, with an ample amount of intercellular spaces, where cells are loosely packed. These cells are made up of cellulose, have large central vacuoles and nucleus.
These tissues play a significant role in process of photosynthesis; it also stores water and nutrients. These tissues are found in stems, roots and leaves. The speciality of parenchymatous cells is that, when they get wounded, they again get convert into meristematic plant tissue to get recovered. Parenchymatous tissues are generally present in the soft or non-woody parts of the plants.
Complex Permanent Tissues
As the name suggests, the complex plant tissues play the important role in complexed functions performed in plants, like in transportation of water, minerals and nutrients to the leaves and other parts. Unlike the simple tissues, complex tissues are made up of more than of cells, though have the same origin and are targeted to perform the same function. These tissues are present in two forms which are Xylem and Phloem.
These cells are helpful in transporting nutrients and water to various parts of the plants. Thre are many elements in these cells like xylem fibres, xylem parenchyma, vessels and tracheids; out of which vessels play a significant role. These vessels are the small tubes that provide the supply of water and minerals in plants and this work is supported by the tracheids.
The only living cells in xylem are the xylem parenchyma that plays the role in storing the food and transporting the water. The xylem fibres function in supporting the plants and trees. Point to note is that xylem is responsible for only vertical conduction (one direction).
Phloem parenchyma, phloem fibres, companion cells, and sieve tubes are the four elements of the phloem. Phloem plays the role in transporting food and nutrients, from leaves to various parts of the plants. The important point to note is that the conduction is bidirectional in the phloem, that is phloem transport the nutrients and minerals in both the directions of the plants.
The sieve tubes are made up of various sieve-tube cells or elements and are responsible for providing organic substances like amino acids and sugars. Companion cells give metabolic support to the cells and consist of a sufficient amount of ribosomes and mitochondria than the sieve tubes cells. The only dead tissues in the phloem are the phloem fibres.