Plant Tissue
Tissue : it is an intermediate substance between cell and organ.The group of cells of similar origin, structure and functions is called tissue.Types of Plant Tissue :
(A) Meristematic tissue :Marismatic tissues give rise to various organs and helps plants to grow. Meristematic tissues are those tissues in which the cells remain forever young and divide actively throughout the life of the plant.
Some features of Meristematic tissues are as follows :
The cells are small and protoplasm fills the cell completely.
Maintenance of the cells requires a balance between two antagonistic processes: organ initiation and stem cell population renewal.
It is round, oval or multi-sided.
The cell wall is a very thin primary cell wall and cytoplasm is homogeneous.
Cell contains dense cytoplasm and a single large nucleus.
There is lack of inter-cellular spaces between the cells.
Apical Meristems : These tissues are found in the root and stem apex and it produces auxin and causes the root to increase its length.
Lateral Meristems : there are two type of secondary meristems which are also called as lateral meristems because they surround the plant stem and cause to grow them laterally.
Intercalary Meristems : They are located at the base of internode. It is capable of cell division and allow to rapid growth and re growth of many monocots. Its importance is for those plants whose apex parts are eaten by vegetarian animals. After being eaten the apex part the plants grow with the help of intercalary meristems only. Like – grass.
(B) Permanent tissue :
Permanent tissue are produced after cell division and differentiation by Meristematic tissues.
Permanent tissues are of following types -
| Simple tissue | If permanent tissue is made up of similar types of cells, it is called simple tissue. |
| Complex tissue | If permanent tissue in which more than one cells work as a unit are as called complex tissue. They are heterogeneous in nature |
Xylem and phloem are the complex tissues which constitute the component parts of the vascular bundle. They are also called vascular tissues.
Xylem :
Xylem is a complex tissue forming part of a vascular bundle. Its main functions are –
Conduction of water and minerals and
Also provide mechanical support.
Primary xylem originates from the procambium of apical meristem
And secondary originates from vascular cambium.
Phloem :
It is composed of sieve elements, companion cells, parenchyma and some fibres.Its main function is to conduct foods prepared by the leaves to different parts of the plant.
Plant Hormones and their functions:
Following hormones are found in plants –
Auxins :
Auxins was discovered by Darwin in the year 1880.
This is the hormone which controls the growth of plants. And they are produced in the stem, buds, and root tips.
Its main functions are –
Enhance stem growth and growth of lateral buds.
Auxin also plays a role in maintaining apical dominance.
It prevents the separation of the leaves.
It saves the crops from falling and It destroys the straws.
Gibberellins :
It was discovered by a Japanese scientist Kurosava in the year 1926.
Its main function are as follows :
It promotes stem elongation.
They are not produced in stem tip.
It motivates the seeds to be sprout.
It increases the activity of cambium in the wooden plants.
It turns the dwarf plants into long plants. And also. It hep in breaking the dormancy of plant.
It helps in creating flowering, Large sized fruits and flowers can be produced by its scattering.
Cytokinins :
It was discovered by z in the year 1955 but it was named by Lethem.
Its main function are as follows:
It promotes cell division and development in the presence of auxins.
It naturally works in coordination with auxins.
Zeatin is a hormone in this class, and occurs in corn
It help in breaking the dormancy of seed.
Enhance RNA and protein synthesis.
Abscisic Acid or ABA :
This hormone was initially discovered by Carnes and Adicote and later on by Waring.
Its main function are as follows:
This hormone is against the growth.
Abscisic acid (ABA), also known as Dormin, Dormic acid (DMA)
It keeps the seeds & bud in dormant condition.
It plays main role in separation of leaves.
ABA functions in many plant developmental processes, including bud dormancy.
It delays in flowering of long day plant.
Abscisic acid is also produced in the roots in response to decreased soil water potential and other situations in which the plant may be under stress.
Ethylene :
This is the only hormone which is found in gaseous form.
Its main functions are as follows:
It helps in the ripening of fruit, the opening of flowers, and the abscission (or shedding) of leaves.
Stimulates leaf and flower senescence
It increases the number of female flowers.
seprates leaves, flowers and fruits.
Florigens :
It is formed in leaves but helps in controlling and/or triggering flowering in plants.
It is also called flowering hormones
It is known to be graft-transmissible, and even functions between species.
Traumatic :
This is a type of dicarboxylic acid.
It helps in fixing the injuries of plants.
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