Plus One Botany Notes Chapter 11 Plant Growth and Development is part of Plus One Botany Notes. Here we have given Kerala Plus One Botany Notes Chapter 11 Plant Growth and Development.
|Text Book||NCERT Based|
|Chapter Name||Plant Growth and Development|
|Category||Plus One Kerala|
Kerala Plus One Botany Notes Chapter 11 Plant Growth and Development
The leaves, flower and fruits of the same tree not only have limited dimensions but also appear and fall periodically and some time repeatedly. The development of the structure are mainly perform two processes, growth and differentiation. It have also includes the factors in developmental process they are intrinsic (internal) and extrinsic (external) in plants.
It regraded by the fundamental and conspicuous characteristics for a living being. The growth is an permanent irreversible size of organs are required to a cell. When the growth are included by the process in which both anabolic and catabolic. It needed a certain energy,
e.g., expansion of the leaf growth.
i. Plant growth generally is indeterminate
Plant growth is unique because plants retain the capacity for unlimited growth throughout their life. This ability of the plants is due to the presence of meristems at certain locations in their body. The cells of such meristems have the capacity to divide and self-perpetuate But in dicotyledonous plants and gymnosperms, lateral meristems, vascular cambium and cork cambium that appear in life.
ii. Growth is measurable.
In a cellular level the consequence of increase in the amount of protoplasm. The growth is measured by a variety of parameters are like increase in fresh weight, dry weight, length, area, volume and cell number, when growth are expressed as increase in cell number, the latter express increase in size.
iii. Phases of growth
The growth are mainly divided into three phases:
The root apex and shoot apex are constantly dividing cells. The protoplasm are present rich in this region cells. They possess large conspicuous nuclei. It having primary cell walls in nature, thin and cellulose with abundant plasmodesmatal connections.The cell proximal to the meristamatic phase of growth for elongation. Increased vacuolation, cell enlargement and new cell wall deposition are the character sties for the phases of cells.
iv. Growth rates
The growth increased per unit time it is termed as growth rate. It is expressed by mathematically. An organism, it having cells are produced by variety of ways in more cells. The arithmetic growth having mitotic division for only one daughter cell then it continues to divide other by differentiates and matures. The simplest expression as obtained by a linear curve is
Lt= L0 + rt
Lt = length at time ‘t’
L0= length at time ‘zero’
r = growth rate / elongation per unit time.
In geometrical growth are having initial growth is slow (lag phase), it increases rapidly there after at an exponential rate (log or exponential phase). The both progeny cells are ability to divide mitotic cell division it do continuously. They having limited nutrient supply. So the growth leading by slow down to a stationary phase.
The exponential growth can be expressed as
W1 = W0 ert
W1= final size (weight, height, number etc.)
W0= initial size at the beginning of the period
r = growth rate
t = time of growth
e = base of natural logarithms
Here, r is the relative growth rate and it measure the ability of the plant to the new plant material. It referred to as efficiency index. W1, is a final size depends on the initial size, W0.
v. Conditions for growth
The water, oxygen and nutrients are very essential for the growth. The cells are grow in size by the enlargement for require water. The extension growth nis help in the turgidity of cells and also the enzymatic activities needed for growth. Oxygen helps for the metabolic growth in growth activities. In nutrients are having (macro and micro nutrients of essential elements) for synthesis of protoplasm and act as source of energy. The every plant organism has an optimum temperature range for its growth. The singals in environmental like light and gravity are also depends at some phases and stages of growth.
Differentation, Dedifferentation and Redifferentation
In root apical and shoot apical having the cells derived meristems and also cambium differentiate for specific function.
This is the cells undergo at a few major changes occur in the structrue in both cell,walls and protoplasm. It is develops very strong, elastic, lignocellulosic secondary cell wall. They carry water to the distance under a extreme tension.
The cell of differentiated is lost of its capacity to divide can regain the capacity of under at a certain conditions,
eg., formation of meristem interfascicular cambium and cork cambium from fully differentiated parenchyma cells.
The product of dedifferentiated cells or tissue when lose the capacity to divide but mature to perform specific function,
eg., secondary cortex and cork.
Sequence of the developmental process in plant cell.
This process is done by the growth and differetiation to controlled by the several intrinsic and extrinsic factors. The plant which follow in different pathways in response of environment or the phases in life to from different kinds of structures is known as plasticity.
Plant growth regulators
The plant growth regulators (PGRs) it is small and chemical composition are very simple molecules. They includes the indole compounds (indole-3-aceticacid, IAA), adenine derivatives (N6-furfurylamino purine, kinetin),carotenoids (abscisic acid, ABA), terpenes (gibberellic acid, GA3) or gases (ethylene, C2H4). It having plant hormones or phytohormones are literature.
Plant growth promoters.
The growth are promoting by such an activities are as cell division, cell enlargement, pattern formation, tropic growth, flowering, fruiting and seed formation, e.g., auxins, gibberellins and cytokinins
Plant growth inhibitors. It plays a important role in plant for response of wounds and stresses of biotic and abiotic orgin. e.g., abscisic acid.
ii. The discovery of plant growth regulators
The coieoptiles of canary grass responded to unilateral illumination by growing towards the light source (phototropism). In addition to auxins the nutrients medium was supplemented with one of the following: extracts of vascular tissues, yeast extract, coconut milk or DNA.
In the figure illustrare that tip of the coleoptile is the source of auxin. Arrows indicate direction of light.
Physiological effects of plant growth regulators
It was the first growth hormone to be discovered form urine of human. But later they found that the plants have the presence of PGR is even known. The auxin chemically known as Indole-3-acetic acid (IAA). It help for the growth of apices in the stems and roots. The other auxins like indole butyric acid (IBA) and synthetic auxins like NAA (naphthalene acetic acid) and 2, 4-D (2, 4-dichlorophenoxyacetic) are produced in it. These are used mainly in the agricultural and horticulture practices.
In buds having the growth of apical are inhibited the growth of the lateral (axillary) buds phenomenon is called as apical dominanace. The auxins are also induce parthenocarpy. e.g., tomatoes. It mostly used for herbicides and auxin are also controls the xylem differentiation and cell division. The cell division are auxins involved in the elongation of the cells in the plants
- A plant with apical bud intact
- A plant with apical bud removed
This is the another type of plant growth regulator. It is also known as weakly acidic growth hormones. There are more than 100 gibberellins reported from widely different organisms such as fungi and higher plants. It represent as GA1, GA2, G3, etc. They produce the plants for wide range of physiological responses in it. It have ability to cause an increase in length of axis for elongation and to improve its shape, e.g., grapes, apple, etc. Gibberellins are also involved in the delay senscence. Gibberellins also promotes bolting (internode elongation just prior to flowering) in beet, cabbages and many plants with rosette habit.
Cytokinins is mainly effect on the process of cytokinesis and it discovered as kinetin (a modified form of adenine, a purine) from the autoclaved herring sperm DNA. In plants are having kinetins are not occur naturally so it happens only the synthesised region were rapid cell division occurs,
e.g., root apices, developing shoot buds, young fruits, etc. It helps for formation of new leaves, choloroplast in leaves, lateral shoot growth and adventitious shoot formation and it overcomes the apical dominance.
It is a simple gaseous plant growth regulator. It helps the plants for synthesised for large amounts by tissues undergoing senescence and ripening fruits. The ethylene influences on the horizontal growth of seedlings, swelling of the axis and apical hook formation indicot seedlings. It mainly effect in the ripening of the fruit. The mostly used ethylene compounds as source is ethephon. It helps to control the ripening of fruits and also accelerates abscission in fruits and flowers likes thinning of cotton, cherry, walnut. They involved in the promotes female flowers in cucumbers yield.
v. Abscisic acid
Abscisic acid is a primary role in regulating abscission and dormancy of buds and seeds. It helps the seeds to the for dessication and other factors unfavorable for growth. Abscisic acid act as a general plant growth inhibitor and also help for the metabolism of plants. The seed germination and maturation takes place in it. it stimulates also the closure of stomata.
They are the plants which grown up by the day time it exceeds length a critical length, i.e., requires longer day light period.
They are the plants which involves the exposure of light in less period than a well defined critical duration, i.e., requires shorter photo period in order to initiate flowering.
They are the plants whose induction of flowering response is not more exposure to night duration, e.g., cucumber, sunflowers, tomato, etc.
It can be said that flowering in certain plants depends not only on a combination of light and dark exposures but also their relative duration. This response of plants to periods of day/night is termed photo periodism. It has been hypothesised that there is a hormonal substance that is responsible for flowering, when the plants are exposed to the necessary inductive photoperiod.
It is the phenomenon that having the flowering is either quantitatively or qualitatively dependent on the exposure to low temperature. They also prevent the precocious reproductive development in the growing season. For example for the vernalisation is seen biennial plants. They are normally flower and dieun the second season, we commonly seen biennials are Sugerbeet, cabbages, carrots, etc.
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