Growth and Development of Plant
We know seeds give rise to seedlings, from seedlings there develops a large plant. Plant produces flowers and fruits. These are all the results of growth and development of the plant. Embryo is present in the seed. Growth of embryo is the germination. So without the growth of embryo germination of seed will not take place. Without germination seedlings will not produce. Without growth of seedlings a large plant will not develop. Without development of a large tree we shall not get flowers, fruits, seeds, wood, crops, or the forest and nothing of this sorts. So growth and development of plant is essential for them so that they can again produce seed to maintain their growing by reproduction. Again the growth and development of plant is essential for all animals including human beings, because with growth and development of plant we will not get anything like - food, medicine, cloths, house building materials and a habitable environment. Growth is a fundamental characteristic of all living organisms. Growth means a permanent increase in shape, size weight and in bulk of a plant or its organ.
Region of Growth: The ideal growing region of plants are its root and shootapex. In root or shoot apex there are apical meristems. This region is also known as primary meristamatic region or primary growth region.
Growth in length: The apical Meristamatic tissue by successive cell divisioncreates new cells. The new cells later on increase in size. In this way by the formation of new cells and their increase in size, the apical parts successively increase in length. Formation of young leaf and bud is also the function of these tissues.
At the top of the root there present a cover like structure, which is called root cap. The cell division region is behind the root cap region. The cell of this region divide rapidly and forms many new cells. Behind the cell division region of elongation. Cells of this region increase in size and volume especially in length, as a result length of root increase. Behind the region of elongation lies the permanent region. Cells of this region are mature and are different is shape and size.
At the top of stem there is a bud called apical bud or shoot apex. Cells of apical bud are meristamatic cells. Therefore this is the cell division region, because cells of this region divide rapidly and increase in number. Behind this region is the region of elongation, as cells of this region rapidly increase in length. Behind this region is the permanent region, cells of this region is mature and are different in shape and size.
The breath of a one-year-old mango tree increases after one year. In this way with the increase in age its breath also increase. Breath of a mature root and stem is increased by secondary growth (lateral growth). Usually secondary growth occurs in gymnosperms and dicot plants. So all the broader plants of the world either gymnosperm or dicot plant. Examples of gymnosperms are Cycas and Pinus. Mangos, Jamboline, Litchi, Shaal, Garjan, Sundary, Teak, Gamari, Karai etc. are examples of dicot plants.
Increase in breath takes place in root and stem by their secondary growth in intrastellar or extrastelar region. First in the intrastelar region of vascular bundles there develops a cambium ring. This cambium ring produces secondary xylem tissue towards the center and secondary phloem tissue towards the periphery. As many secondary xylem and secondary phloem is formed from the cambium ring so much increase the breath. Secondary growth also takes place in extrastelar region (out side the pericycle).
We came to know that apical region of stem is the ideal region of growth. During apical growth there develops young leaves and sometimes axillary bud. Always the rate of development of axillary bud is lesser than that of apical bud. It is observed that if the apical bud is removed the growth of axialiary bud expedite. For production and better growth of buds at the lower region in many cases the apical bud is removed. In Tea plant if apical bud is removed many axillary buds produces. In this way the tree characterstics of tea plants changes to shrubby nature, and production of bud therefore, the production of tea increases. By the influence of apical bud usually the production of axillary bud seized, or if produce always the growth of axillary bud is dominated by the growth of apical bud. The dominating tendency of apical region of stem is called apical dominance.
The growth regulatory substance named Auxin mostly present at the shoot apex, for which growth rate is higher at this region. When apical bud is removed Auxin flows downwardly, thus produces axillary bud or accelerate their growth.
You can demonstrate the apical dominance very easily. Cut the apical bud of a potted chili or ornamental plant. Then it will be observed that the axillary buds developed to branches. Without cutting the apical bud not much branching will occur.
Growth regulatory Substances: Growth Regulators
There are some biochemical substances, small amount of which regulate the growth of plants. These substances are produced in the plant bodies. As they regulate the plant growth so they are called growth regulators. Earlier they were called Hormone. As they are produced in plants they are now named phytohormone. Phyto- means plant.
Growth regulators are divided mainly into two types: -
(1) Growth promoter and (2) Growth inhibitor.
Growth promoters are Auxin, Gibberellin, Cytokinin and Flowering hormone. And Growth inhibitors are Dormin or absecic Acid.
Influence of Auxin : (i) Auxin increases the length of the cell, (ii) Produce apical dormancy (iii) Initiates the formation of root, (iv) Help to produce seedless fruits.
Uses of Auxin: (1) Used for germination of seeds (2) As Auxin Initiate rootformation so it is used in grafting of mango, litchi, Psidium etc. plants. (3) It used in case of early fruit fall. (4) Auxin also used in production of seedless fruits, in floriculture, tissue culture and in management of weeds.
Influence of Gibberellin: (1) Gibberellin increases the length of stem. Breaksthe dormancy of seeds and buds (3) Help to bloom the flower.
Influence of Cytokinin: Cytokinin accelerates cell division.
Uses of Cytokinin: (1) Used for production of seedless fruits (2) In tissueculture.
Abscisic Acid: Leaves and buds droped by its influence. inhibit growth of bud.