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This is a property of the protoplasm also. A Photonasty The nastic movement caused in response to light is called photonasty or photonastic movement. Each slip gives rise to a new plant. These make use of the food substances of the root cells and secrete a pinkish pigment called leghemoglobin which is an oxygen carrier like hemoglobin. Zinc Zinc is involved in the synthesis of indole acetic acid by activating the enzyme tryptophan synthetase. These include some bacteria and blue-green algae, which have acquired the capaicity to fix atmospheric nitrogen during the evolutionary process by possessing a set of genes called 'nif ' Nitrogen fixing genes. Why is the cell called a physiological unit?
Lignin and cellulose have affinity for water. This is called a. The transpiration pull theory was supported by a. Renner b. Curtis c. Clark d. All the above Two Marks 1. Explain the mechanism of stomatal opening and closing. Describe the Proton - potassium pump hypothesis. Demonstrate root pressure with the help of an experiment.
Give an experiment to demonstrate cohesion - tension theory. Explain the objections to the root pressure theory.
Give an account of the inherent properties of the leaf which affect the rate of transpiration. Written an essay on the theories explaining mechanism of stomatal movement. Give an account of the factors influencing stomatal movement. Explain the postulates of the cohesion - tension theory. Add a note on the objections and explanation.
List and explain the factors affecting transpiration. Give an account of the various theories explaining the ascent of sap.
Mineral Nutrition Mineral nutrition of plants was a phenomenon known from very ancient times. Woodward observed for the first time that plants grow better in muddy water than rain water. Later it was proved that minerals have specific functions in plant metabolism.
When this ash was analysed it was found to contain 40 elements besides C,H,O,N and S which were oxidized. All these are not essential for plant nutrition but on analysis the important essential elements have been identified and based on their role in plant metabolism and requirement, they have been classified as major elements and trace elements. The functions of the various minerals in general depends on the role of the mineral in plant metabolism.
Criteria for Essentiality of a Mineral Element Essential elements should have the following characteristics i. Normal growth and reproduction must be dependent on particular mineral elements. An essential element must have direct influence on the plant. Essential elements must be indispensable and their substitution by other elements must be impossible.
Some elements are required in very low quantities and the status of essentiality or non essentiality is doubtful. For example silicon. Functions of Minerals i Mineral elements are constituents of the various parts of plant body, for example calcium which is found in the middle lamella, nitrogen and sulphur in proteins, phosphorus in nucleic acids. Hydroponics The term hydroponics has been used for growth of plants in water culture. This may also be referred to as soil-less agriculture, test-tube farming, tank farming or chemical gardening.
Commercially hydroponic cultures are maintained in large shallow concrete, cement wood or metal tanks in which gravel and nutrient solutions are taken. The tanks are provided with pumps and empty auxiliary tanks to pump out and circulate the growth solution and to maintain proper aeration of the nutrient solution.
The technique of hydroponics is employed to know which mineral element is essential for the growth and development of the plant. Commercially the application of hydroponics involve the production of horticultural and floricultural crops.
This method may be used to increase yield of ornamentals such as gladioli, snapdragon, roses and vegetables such as carrot, radish, potatoes, tomatoes and lettuce. Advantages of Hydroponics i. It is possible to provide the desired nutrient environment. The acid-base balance can be easily maintained. Mulching, changing of soil and weeding are eliminated.
Proper aeration of nutrient solution is possible. Labour for watering of plants can be avoided. Tilling is not necessary. Production is limited when compared to field conditions. Technical skill is required to design equipment. If a disease appears all plants in the container will be affected. Can be used only for short duration. Essential Major Elements and Trace Elements The plant ash reveals the presence of 40 elements but all are not essential for plant nutrition, only a few are essential for growth and development of plants.
These are called the essential elements. The essential elements may be grouped as major elements or macronutrients and trace elements or micro nutrients, based on their requirement by plants. Major elements or Macro Nutrients These elements are required in large amounts and form the plant consituents. The major elements are otherwise known as macronutrients.
These include carbon, hydrogen, oxygen, nitrogen, phosphorus, potassium, calcium, magnesium and sulphur. These elements form an integral part of complex organic molecules. Some of these elements help in the functioning of enzyme systems. The sources of macronutrients are generally the soil or the atmosphere. Carbon is got from carbodioxide of the atmosphere. Oxygen is derived from water and atmospheric oxygen.
Nitrogen is present in the atmosphere as an inert substance which is brought to the soil and converted to soluble nitrates either by asymbiotic or symbiotic nitrogen fixation. Phosphorous and sulphur and derived from rocks during weathering. The source of hydrogen is water. Trace elements or Micronutrients Elements like iron, boron, managanese, copper, zinc and molybdenum are required for plants only in very small amounts but these are indispensable for the normal growth and development of plants.
They are a part of carbohydrates, proteins, and fats. Thus these elements have a role to play in the general metabolism of plants. Deficiency symptoms Deficiency of these elements is very rare because the plants have a steady supply of these through water and gaseous exchange.
Deficiency affects the normal growth and developments of plants. Nitrogen Nitrogen is an essential constituent of proteins, nucleic acids, vitamins and many other organic molecules such as chlorophyII.
Nitrogen also forms a constitutent of various hormones, coenzymes and ATP. Deficiency symptoms i Stunted growth ii Chlorosis iii Reduction in flowering iv Excessive colouring in apple and peach and reduction in fruit size. Phosphorus It is present in plasma membrane, nucleic acids, nucleotides, many co-enzymes and organic molecules. It plays an important role in energy metabolism. Phosphorus promotes healthy root growth and fruit ripening.
Deficiency symptoms i. Loss of older leaves ii. Reduction in growth iii. Increase in phosphatase enzyme activity iv. Causes accumulation of carbohydrates in soyabean 4. Potassium Potassium is required in the meristematic regions and regions of cell differentiation. It accumulates in older leaves. Though it does not have a structural role, it is involved in stomatal opening and closing. It is an activator of many enzymes and has a role in protein and carbohydrate metabolism.
Leaf tips curve downward ii. Causes mottled chlorosis iii. Development of chlorosis at tips and margins of leaves. Shortening of internodes and stunted growth. Sulphur Sulphur is the constituent of certain vitamins such as thiamine and biotin. It is constituent of coenzyme - A playing an important role in respiration. It forms the sulphydryI group in many enzymes and is a constitutent of sulphur containing aminoacids such a cystine, cysteine and methionine. Causes inhibition of protein synthesis.
Younger leaves show chlorosis first iii. Chloroplasts of mesophyII show a decrease in stroma lamellae but grana increase. Magnesium Magnesium is a constituent of chlorophyII molecule which cannot be formed without magnesium. It has a vital role in carbohydrate metabolism and the binding of ribosomal sub-units. Interveinal chlorosis takes place. Anthocyanin pigment deposition takes place after chlorosis. Necrotic spots appear in acute cases.
Calcium Calcium forms an important constituent of the cell wall occurring in the middle lamella as calcium pectate. It has an important role in the formation of plasma membrane.
Calcium plays a role in mitotic cell division and is a constitutent of enzymes like phospholipase and adenyl kinase where it acts as an activator. Affects the carbohydrate metabolism. The process of respiration is badly affected as number of mitochondria are decreased.
Meristematic tissues are affected and leaf and root tips die. Cell wall may become brittle or rigid. Micro Nutrients 8.
Iron Soil is generally not deficient in iron. Iron is a constituent of various flavoproteins and forms a part of enzymes such as catalases, peroxidases and cytochromes. It plays an important role in the electron transport system of photosynthesis being part of cytochrome and ferredoxin.
Causes interveinal chlorosis and the leaves become yellow or white. Impairs aerobic respiration and related processes. Fruit trees particularly show sensitivity to iron deficiency. Boron Leaves and seeds require boron. It plays a role in nitrogen metabolism, hormone and fat metabolism.
It causes brown heart-rot disease in beetroots. In apple internal tissues become corky. Causes leaf to curl and become brittle. Premature fall of fruits and flowers. Managanese Managanese is required by leaves and seeds. It is an activator of enzymes like carboxylases, oxidases, dehydrogenses and kinases. Causes grey spot disease in oat.
Poor development of root system. Interveinal chlorosis occurs. Copper This is required in all plant parts. Copper forms a component of enzymes such as phenolases and tyrosinase. Copper being a constituent of plastocyanin plays a role in photophosphorylation. Copper maintains the carbohydrate - nitrogen balance. Causes die back of shoots especially in Citrus. Reclamation disease is caused in plants growing on newly reclaimed soil where seed formation is affected.
Zinc Zinc is involved in the synthesis of indole acetic acid by activating the enzyme tryptophan synthetase. It plays a role in protein synthesis.
It acts as an activator of many other enzymes such as carbonic anhydrase, alcohol dehydrogenase, hexokinase and so on. Causes distortion of growth. Leaves become very small and rosetted called as little leaf disease. Interveinal chlorosis and stunted growth of stems is seen. Molybdenum Molybdenum has an important role to play in the metabolism of nitrogen.
It affects the synthesis of ascorbic acid. It activates the enzymes involved in nitrogen metabolism. Hydroponics is otherwise called a soil-less agriculture b tank farming c chemical gardening d all the above 2. This element is a constituent of chlorophy11 a Manganese b Magnesium c Potassium d Zinc Fill in the blanks 1.
Exanthema is a disease caused due to deficiency of Deficiency of Molybdenum causes Sulphur containing amino acids are Explain the advantages and disadvantages of Hydroponics. Describe the technique of hydroponics with a diagram.
Describe the criteria for essentiality of an element. Explain the role and deficiency symptoms of any three macronutrients. Describe the deficiency symptoms of copper, boron and molybdenum. Write an essay on the role and deficiency of macro and micronutrients.
Theories of Translocation Plants absorb minerals from the soil and translocate them to other parts of the body. Minerals are absorbed in the form of soil solution contained in the pore spaces between the soil particles and the root hair. The soil solution contains the mineral salts in the dissolved state.
Several theories have been put forth to explain the mechanism of translocation of mineral salts. These theories can be placed under two headings i Passive absorption and ii Active Absorption which can be further subdivided as follows. Passive Absorption When the movement of mineral ions into the roots occurs by diffusion without any expenditure of energy in the form of ATP it is called Passive Absorption. This form of absorption is not affected by temperature and metabolic inhibitors.
Rapid uptake of ions is observed when a plant tissue is transferred from a medium of low concentration to a medium high concentration. Various theories have been put forward to explain mineral salt uptake by passive absorption. The anions and cations within the plant cells are exchanged with the anions and cations of equivalent charge from the external medium in which the cells are kept.
This mechanism can be explained by two theories. According to this theory ions are transferred from soil particles to root or vice versa without passing into solution. These ions oscillate within a small volume of space called oscillation volume. Donnan in which the fixed or indiffusible ions play an important role. These ions are present on the inner side of the cell and cannot diffuse out. When a cell having fixed anions is immersed in sals solution, anions equal in number and charge to the fixed ions move into the cell.
To balance the negative charges of the fixed ions additional cations also move into the cell and the cell sap cation concentration becomes higher than the external medium. This is called Donnan Equilibrium. In the same way if there are fixed cations, additional anions will accumulate from the external medium.
Active Absorption The absorption of ions against the concentration gradient with the expenditure of metabolic energy is called active absorption. The mechanism of active absorption of salts can be explained by several theories.
The carrier may be an enzyme or a protein. Metabolic energy is expended in this process. This concept is supported by Isotopic exchange using radioactive isotopes, saturation effect and specificity of carriers. The carrier concept is explained by two theories: Lecithin which carries both anions and cations and forms a lecithin- ion complex. Lecithin is regenerated with the help of enzymes Choline esterase and choline acetylase.
This requires expenditure of metabolic energy. Lundegardh who suggested that anions could be transported across the membranes by cytochrome system utilising energy released by direct oxidation of respiratory intermediates. The important postulates are: Therefore this theory explains respiration due to anion absorption which was called anion respiration or salt respiration. Translocation of Solutes In higher plants food is synthesised only in the green leaves which are the sites of Photosynthesis.
From here the food is traslocated to the different parts of the plant in the soluble form. Therefore thisis also referred to as translocation of solutes. Direction of translocation Translocation of food occurs in the downward upward and lateral directions.
Down ward translocation Downward trnaslocation takes place from the leaves downwards to the stem, roots and storage organs. Upward translocation In some stages of plant life such as seed germination, emergence of new shoots from underground storage organs and development of buds, flowers and fruits, the food materials are translocated upward.
Lateral translocation In certain parts of stem and roots food is translocated in lateral direction through medullary rays. The portion from where tissues are removed is sealed with melted wax. After 7 or 8 days the epidermis and cortex of upper portion of the ring become very much swollen and from this swollen part the adventitious roots emerge out. It happens because the food material translocated from the leaves does not pase through the ring and is stored in the upper portion.
Mechanism of Translocation Following theories were proposed to explain the mechanism of translocation of solutes. Based on this Munch in proposed a hypothesis according to which the soluble food materials in the phloem show mass flow. The fundamental idea behind this hypothesis is that the sugars synthesized by mesophyll cells of leaves increase the osmotic pressure OP of these cells causing entry of water into mesophyll due to absorption of water by the xylem cells of root.
In other words a turgor pressure gradient exists through phloem, between the source which is the mesophyll cell and the sink which refers to regions of requirement. As a result, the turgor pressure of mesophyll cells increases on the upper side which forces the solutes dissolved in water to flow en masse into the phloem of stem and finally into the roots.
This can be explained by a physical system. It consists of a glass tube bent at right angles. At the two ends differentially permeable membranes are tied.
The two osmometers are kept in two separate water containers connected with each other through a tube. The most important objection for this hypothesis is that it explains only unidirectional flow of solutes.
Phloem loading is caused by movement of photosynthates from mesophyll to phloem. Unloading of phloem is caused by movement of photosynthates from phloem to other parts where required. This is the source-sink relationship. It is an important mineral present in the bodies olf living organisms. It forms a component of proteins and aminoacids and is also present in nucleic acids, cytochromes, chlorophyll, vitamins, alkaloids and so on.
Nitrogen cannot be used directly and is converted to Nitrites, Nitrates and Ammonia by a process called Nitrogen Fixation. There are many free living organisms like bacteria and blue-green algae which are involved in nitrogen fixation.
The ammonia and urea present in the soil are directly absorbed by plants. Nitrogen Cycle The atmosphere is the source of elemental nitrogen which cannot be used directly by plants.
The atmospheric nitrogen is converted to ammonia, nitrite, nitrate or organic nitrogen in the soil. The death and decay of organic systems causes cycling of ammonia from amino acids, purnies and pyrimidines. Some of these forms may also be converted to Nitrogen gas and may be cycled back into the atmosphere.
The process by which these forms get inter converted to maintain a constant amount of nitrogen in atmosphere, by physical and biological processes is called nitrogen cycle.
Ammonification ii. Nitrification iii. Nitrate assimilation iv. Denitrification and v. The sources of organic nitrogen in the soil are animal excreta and dead and decaying plant and animal remains which are acted upon by ammonifying saprotrophic bacteria such as Bacillus ramosus, Bacillus vulgaris, certain soil fungi and actinomycetes.
Nitrifying bacteria like Nitrosomonas convert ammonia to nitrite and another bacterium called Nitrobacter converts nitrite to nitrate. But is cannot be used by plants directly. So it is first reduced to nitrite by the enzyme nitrate reductase. Nitrite is then converted to Ammonia by the enzyme nitrite reductase series of steps requiring a total of eight electrons provided by reduced NAD and Ferredoxin Fd.
This reduction of Nitrate of Ammonia and its incorporation into cellular proteins by aerobic micro organisms and higher plants is called nitrate assimilation. This process ends in the release of gaseous nitrogen into the atmosphere and thus completes the nitrogen cycle.
A number of bacteria such as Pseudomonas denitrificans, Bacillus subtilis and Thiobacillus dentrificans are involved in this process. Biological Nitrogen Fixation Nitrogen fixation that takes place by living things is called biological nitrogen fixation. These include some bacteria and blue-green algae, which have acquired the capaicity to fix atmospheric nitrogen during the evolutionary process by possessing a set of genes called 'nif ' Nitrogen fixing genes.
They fix Nitrogen as given in the 6e following reaction. Non-Symbiotic Nitrogen Fixation This is carried out by free living organisms in the soilsuch as Bacteria, blue green algae. Bacteria include aerobic bacteria such as Azotobacter and anaerobic baceria such as Clostridium, Chlorobium and Chromatium. These organisms contain an enzyme system called Nitrogenase which is a Mo- Fe Molybdenum-ferredoxin protein. A symbiotic association is a mutually beneficial relationship between two living organisms which are called symbionts.
Nitrogen fixation in non-legumes An actinomycete like Frankia establishes a symbiotic relationship with roots of higher plants such as casuarina and Alnus. Blue-green algae like Nostoc establish symbiotic relationships in the corolloid roots of Cycas, or thalli of Anthoceros. Nitrogen fixation in legumes This is the commonest type of symbiotic nitrogen fixation which has been elaborately studied.
A soil bacterium called Rhizobium infects roots of leguminous plants belonging to Family Leguminosae and forms the root nodules. The bacteria living in the soil enter the root hair and penetrate the root cortex through an infection thread. When the bacteria enter the cortical cells of roots, the latter get stimulated to divide vigorously and form nodules on the root.
The bacteria come to occupy the nodules, and at this stage lacl a rigid cell wall being called bacteroids.
These make use of the food substances of the root cells and secrete a pinkish pigment called leghemoglobin which is an oxygen carrier like hemoglobin. The Rhizobia in the form of bacteroides contain the enzyme nitrogenase which is responsible for fixation of Nitrogen thus benefitting the host plant. Leghemoglobin is supposed to protect the nitrogenase enzyme as it can function only under anaerobic conditions.
Major Nitrogen-fixing Biological Systems. The theory explaining passive absorption of mineral salts is: Ion exchange b. Carrier Concept c. Cytochrome pump theory d. None of the above. Contact exchange theory was put forward by: Jenny and Overstreet b. Hylmo and Kramer c. Bennet and Clark d. De Vries and Curtis Fill in the Blanks 1. The bacterium involved in symbiotic nitrogen fixation is The nitrifying bacteria are Explain the theories of active transport of mineral salts.
Describe the transports of mineral by ion exchange. Write notes on the cytochrome-pump hypothesis of mineral salt transport. Describe the ringing experiment to demonstrate translocation of solutes. Write an essay on the theories of mineral salt absorption. Describe the Nitrogen cycle. Explain biological Nitrogen fixation. Plant Movements Plants are sedantary living things generally lacking the power of locomotion. But they possess the property of irritability i.
This causes some kind of movement in plants, which is generally a very slow movement and often escapes notice by the human eye. But these movements can be actually demonstrated by a technique called time - lapse motion picture photography or by simply observing the plant at intervals of several hours and noting the changes in positions of the plant organs. The movements showed by plants can be classified broadly as 1 Hygroscopic- due to loss or gain of water and 2 Vital-due to irritability of the cytoplasm.
The vital movements may be further subdivided as follows. Movements of Locomotion These are generally very fast movements which may be A autonomic or Spontaneous and B induced or Paratonic. These movements are very common among lower plants and mostly exhibited by unicellular organisms.
These movements are relatively faster and more pronounced. A Autonomic Movements: The spontaneous locomotory movements may be i Ciliary: B Paratonic movements The induced locomotory movements are also called tactic movements induced by external stimuli.
Based on the nature of stimuli, these may be of three types: Seen in zoospores and gametes which are provided with a light sensitive eyespot which is attracted by low light intensities.
Movement in response to heat stimulus is seen in certain motile algae like Chlamydomonas which moves from a colder to a warmer place. In bryophytes and pteridophytes, the swimming antherozoids are attracted towards the archegonium by chemical stimuli such as organic substances like sugar, malic acid and so on. These can change or move the position of their organs by means of curvature. These types of movements may be further classified as A Movements of growth and B Movements of Variation.
A Movements of growth: There is a change in the position of the organ either due to increase in number of cells or enlargement of cells or both. These movements can be Spontaneous or Autonomic and Induced or Paratonic.
These include the 1 Nastic and the 2 Nutational movements 1 Nastic Movements These movements are generally observed in leaves, flowers, petals and bud scales. In these structures at some stage of development, growth in one surface is more than the growth on the other surface. There may be two types of such movements: If the upper or inner surface has more growth, the movement is called epinasty.
An example for epinasty is the opening up of a Fig. This indicates rapid growth on the abaxial or lower side of an organ. An example for this is the unfolding of a fern frond and closing of a flower. In tendrils and runners, there is a spiral type of growth of the stem apex called circum Tendril nutation. Ordinarily, nutational movements occur due to alternate change in the opposite sides of the apex. These movements are very Fig.
The stimuli are effective in causing growth movements only when they are unidirectional. Such movements are generally known as tropic movements and the phenomenon is referred to as tropism. Based on the nature of stimulus, tropisms may be of various types. Plants show five different types of geotropic responses. Experiment to demonstrate negative geotropism in aerial stems The effect of gravity on the plant can be demonstrated using an apparatus called klinostat.
The klinostat has a rotating pot like container mounted on an axial rod. A potted plant is fitted horizontally on the klinostat and is slowly rotated at about four rotations per hour.
By this, the effect of gravity is completely eliminated, as all the sides of the plant are equally stimulated by gravity. This proves that the stem tip is negatively geotropic.
Some of the plant parts such as stems, branches, leaves and, pedicels of flowers move towards the stimulus of light and are said to be positively phototropic while others such as roots and rhizoids which move away from the stimulus of light are said Rotating to be negatively phototropic. Later on F. Went in , suggested the involvement of auxins in this phenomenon.
Klinostat Experiment to demonstrate positive phototropism in shoot tips A darkened black box is taken having a small window at one side. A well-watered potted plant is placed inside the box. The is referred to as a Fig. If the window is kept opened, it is found after two days, that the shoot tip bends and grows towards light proving that it is positively phototropic.
These may be divided into two types. Terminal i Autonomous Turgor Movements leaflet These do not require any stimulus and are observed in the Indian Telegraphic plant - Desmodium gyrans. Here the compound leaf shows three leaflets, one terminal large leaflet and two very small lateral, opposite leaflets.
The two lateral leaflets show rhythmic Lateral movements during the day. These move leaflet up, then move back, and then move down finally back to the original position. This type of movement is due to variation or change in the turgor pressure at the base Fig. Indian Telegraphic plant ii Paratonic or induced turgor Leaves unfolded Leaves folded movements These are turgor movements induced by stimuli such as light, temperature and contact.
These movements are also called Nastic movements and may be of various types such as i Siesmonasty ii Nyctinasty Fig. The best example is Mimosa pudica Touch - me - not plant which is the sensitive plant. This effect is caused by a change in the turgidity of the leaflets brought about day-leaves Night by the movement of water into and out of the open leaves parenchymatous cells of the pulvinus or folded swollen leaf base.
Entry Fig. The nyctinastic movements may be of two types. A Photonasty The nastic movement caused in response to light is called photonasty or photonastic movement. The opening of leaves and flowers during day time and their closure at night is an example. The leaves of Oxalis show such a type of sleeping movement. B Thermonasty The nastic movement taking place in response to temperature is called Thermonasty or thermonastic movement.
In Crocus, the flowers open at high temperature and close at low temperature. Differences between tropic and nastic movements. Tropic Movements Nastic Movements 1 The movements occur due to a These movements occur due to a unidirectional stimulus diffuse stimlus 2 The stimlus acts on protoplasm The stimlus acts on the protoplasm from one direction only on all sides 3 The response is directly related The response has no relation with the to the direction of the stimulus direction of the stimulus but with the organ 4 These are movements of curvature These are also movements of caused by unilateral growth curvature but they are caused by reversible turgor changes.
Hygroscopic movements are related to a Loss of water b Gain of water c Both d None of the above 2. This is an autonomic movement of locomotion a Phototactic b Phototropic c Photonastic d Ciliary 3. Epinasty is a movement of a Curvature b Locomotion c Growth d None of the above 4.
Reversible turgor changes are common in a Nutational movements b Tropism c Tactic movements d Nastic movements 5. Negative geotropism is not exhibited by a Roots b Stems c Sporangiophores of fungi d Pneumatophores of mangroves Fill in the blanks 1. Siesmonasty is exhibited by the Desmodium gyrans shows Geogropism in shoots can be demonstrated using a Rhizomes which run at right angles to force of gravity show Describe autonomous movements of locomotion.
What are the paratonic locomotory movements. Explain the spontaneous growth movements. Give an account of geotropism in aerial shoots. Describe an experiment to demonstrate phototropism. Differentiate between tropic and nastic movements. Ten marks 1. Write an essay on movements of locomotion.
Describe the turgor movements in detail. Reproduction in Angiosperms 1. Vegetative Propagation Generally Angiosperms propagate by producing seeds, which is the result of sexual reproduction.
However they resort to other methods of reproduction, such as vegetative propagation. Plants belonging to this category propagate by a part of their body other than the seed.
The structural unit that is employed in place of seed is called propagule. Lower plants reproduce vegetatively through budding, fission, fragmentation, gemmae, resting buds, spores etc.
Methods of vegetative propagation have been further divided into two types. A Natural vegetative propagation and B Artificial vegetative propagation A. Natural Methods of Vegetative Propagation Vegetative Propagation by Roots Some modified tuberous roots can be propagated vegetatively, when planted in soil. The buds present on the roots grow as leafy shoots called slips above ground and adventitious roots at their bases.
Each slip gives rise to a new plant. Sweet potato, Topioca, yam, Dahlia and Tinospora.
Adventitious buds develop on the ordinary roots of Dalbergia sisoo, Populus, Guava, Murraya sp, etc. Vegetative Propagation by Stem In many plants, stem is modified to perform different functions. The modified stems perform three distinct functions a perennation, b vegetative propagation and c storage of food. Modified stems which help in propagation can be classified into following three categories: Underground 2.
Subaerial 3. These store reserve food, propagate vegetatively and are adapted for perennation. They give rise to aerial shoots that grow actively during favourable conditions. On the approach of unfavourable conditions, the aerial shoots die. The underground stems remain dormant during the unfavourable conditions. Once the conditions become favourable, they produce new aerial shoots. The various types of underground stems are 1. Rhizome, 2. Tuber, 3. Bulb, 4. Corm Bulb The stem is shortest and somewhat disc-like and does not contain any food material.
Stem is covered by numerous thickened, overlapping leaves or leaf bases usually called scales. The whole structure takes the form of a bulb. The short and reduced stem bears numberous adventitious roots at its base: In this case, the fleshy scales completely surround the reduced stem forming the concentric layers around stem forming the concentric layers around one another. On the outside they are covered by a few dry scales forming a membranous covering, called the tunic.
The fleshy scales are bases of the foliage leaves, eg. Here, the leaves are small and scale-like and only overlap at the margins. There is also no outer tunic. The scaly bulbs are found in lilies, garlic, etc. These develop into new bulbs or on separation from the parent bulb develop into new plants. They serve both for food storage and vegetative propagation.
Corm It is more or less a condensed form of rhizome. It is a short, stout, solid and fleshy underground stem growing in the vertical direction.
It is more or less rounded in shape or often somewhat flattened from top to bottom. It contains excessive deposits of food material and grows to a considerable size.
It bears one or more buds in the axil of scale leaves and some of these buds grow up into aerial flowering shoots and from the base adventitous roots pass into the soil. Food materials get stored in the basal portion and in this way a new corm is formed. Colocasia, Amorphophalus etc.
Propagation by Modified Subaerial Stem These modifications are found in many herbaceous plants with a thin, delicate and weak stem. In such plants a part of the stem lives under-ground whereas remaining part of the stem is aerial. These plants bear adventitious roots and aerial branches at nodes. Such plants propagate quickly with the help of fragments of special branches. Subaerial modified stems are of the following types: Stolon, 2.
Stolons These develop from underground stems. They grow horizontally outwards and bear nodes and internodes. They resemble the runners except that they are produced just below the surface of the soil, eg.
Offset These are also known as condensed runners. Unlike a runner, an offset produces a tuft of leaves above and a cluster of roots below. On breaking off from the parent plant, each branch forms an independent plant. Propagation by Leaves Leaves are not a common means of vegetative propagation in nature. However, Bryophyllum is known for its remarkable ability to reproduce by leaves. In Bryophyllum plantlets develop from the buds present on the marginal notches of the intact leaves. These plantlets become detached and develop into independent plants.
Propagation Through Bulbils These are spherical multicellular, fleshy buds produced in the axil of foliage leaves in the place of axillary buds. They grow to form new plants, when shed and fall on the ground. Dioscorea, Oxalis, Pine apple, etc.
Propagation by Turions These are special type of fleshy buds that develop in aquatic plants. Potamogeton, Utricularia, etc. Horticultural importance of Natural vegetative propagation Agriculturists and horticulturists use various means of natural vegetative propagation explained above for raising crops and garden plants for commercial purposes. The chief advantage of vegetative propagation is the perpetuation of the desirable features of a selected plant. We are familiar with the fact that potatoes are propagated by whole tubers or their pieces, ginger and banana by the division of rhizomes, Colocasia and Crocus by the pieces of corms, onion and garlic by bulbs, mint and chrysanthemum by suckers and sweet potatoes by the pieces of tuberous roots.
Artificial Method of Vegetative Propagation In addition to the natural methods of vegetative propagation as described above, several artificial methods of vegetative propagation are practised. Following are the important artificial methods of vegetative propagation.
Cuttings The portion of any plant organ such as stem, root or leaf, used for vegetative propagation is called cutting. Stem cuttings are most commonly used for this purpose. Factors such as the optimum length and diameter of the cutting, age of the parent plant and season are to be considered, while selecting a cutting for each species.
Some of the plants propagated by stem cuttings are sugarcane, rose, Bongainvillaea, Moringa, Hibiscus, Thepesia etc. Grafting It is the most common method of vegetative propagation. In this method part of two plants are joined in such as way that they grow as one plant. Grafting is done between the two closely related dicotyledonous plants having vascular cambia. The rooted supporting portion of one plant, called stock is joined with a twig of another plant called scion.
Advantages of Vegetative propagation Vegetative propagation has a number of advantages. Some of these are as follows: Vegetative propagation is a more rapid, easier and a less expensive method of multiplying plants which have either poor viability or prolonged seed dormancy.
It also helps us to introduce plants in new areas where seed germination fails to produce plants due to change in the soil and environmental conditions. Plants like Bermuda grass or doob grass Cynodon dactylon , which produce only a small quantity of seeds are mostly propagated vegetatively. Vegetative propagation is the only known method of multiplication in plants like banana, seedless grapes and oranges, rose and jasmine that have lost their capacity to produce seeds through sexual reproduction.
Grafting permits the physical and physiological joining of separate individuals for the best economic advantage i. The good qualities of a race or variety can be preserved indefinitely.
The greatest advantage of vegetative propagation is that all plants produced will have the same characters and hereditary potential as the parent plants. It is not possible in the plants raised from seeds, since it contains blended characters of both the parents.
In Hibiscus vegetative reproduction takes place by a. Stem b. Bud c. Rhizome d. The plant which propagate with the help of its leaves is a. Onion b.
Cactus c. Potato d. Bryophyllum Fill in the blanks 1. During grafting the part that becomes the supporting portion is called as A piece of potato tuber can form a new plant if it has Two Marks 1. What is grafting? What is a bulbil? Differentiate between stolon and sucker. Why is grafting not possible in monocot plants? Discuss the significance of vegetative propagation 2. What is vegetative propagation? Give a brief account of vegetative propagation 2.
Describe different means of natural vegetative propagation. Micropropagation Micro propagation is a rapid method of vegetative multiplication of valuable plant material for agriculture, horticulture and forestry. In this process, a large number of plantlets are produced from a small mass of explanted plant tissue by the tissue and cell culture technique.
The ability of every living plant cell to produce the entire plant is called totipotency. This is being exploited industrially to multiply plants which are difficult to propagate by conventional means.
Procedure for micropropagation In this method, a small segment of explant is cultured in a nutrient medium; the explant may be a meristametic tissue of a stem tip, an inflorescence etc. The explant tissue produces callus during the period of incubation. After the production of enough amount of callus tissue, the callus is sub-cultured in a fresh M. Medium containing growth hormones auxin and cytokinin. The sufficiently developed calluses are then transferred to regeneration medium where the calluses are induced to produce roots and shoots.
After the proper development of roots and shoots, the individual planets are transferred to pots in a green house for further existence. Sometimes the callus tissue can be homogenised and the homogenate is directly plated on the medium. The cell masses of the homogenate grow and produce new plantlets. Multiple Shootlet Production This process is adapted to produce multiple copies of a desirable plant by making use of shoot tips. The desirable plant is multiplied for being a rare hybrid or a sterile plant with unusual features or for obtaining individual plants of only one sex.
In this process multiple buds are formed from the cultured shoot tips without intervention of a callus in response to specific treatments. These buds are grown into shoots and are subsequently induced to produce roots with the rooting hormones. The shoots are then planted in the soil to develop into new plants. The chief advantage of this technique is the large scale cloning of plants throughout the year in a very small space. More examples of micropropagation on a commercial scale have been reported in Potato, Bananas, Begonias, Chrysanthemums, etc.
Somatic Embryogenesis Somatic cells are cultured in electric shakers to obtain single cell suspensions. After sometime when the number of cells has increased to a maximum depending upon the amount of the nutrient medium, the culture is made stationary.
Each cell starts differentiating into an embryo and proceeds through globular heart-shaped and torpedo shaped stages resembling the development of sexually produced embryos.
Since these embryos develop from the somatic calls, they are called as embryoids. Thousands of somatic embryos embryoids can be produced in a small volume of the nutrient medium contained in a culture tube. Each of these embryoids can form a complete plant with a normal tap root system.
Success has been achieved in Carrot, Celery and Alfalfa Micropropagation can be practiced in plants for many reasons 1. In some plants, seed production may be difficult or impossible. In such cases micro propagation is an effective technique for producing a large number of identical clones. In some plants, normal sexual reproduction can take place, but only a small number of hybrids show the desired characters.
The individuals resulting from micropropagation are all identical; they show a number of desired characters. Sometimes a plant of desirable genotype may be required for planting. In plants like oil palms, identical clones are produced through micropropagation.
It is a standard multiplication method by which all the individuals produced are protected against mutation. Till , more than sixty species of forest trees were bred by using micro propagation.
Define totipotency. What is Micropropagation? Write an essay on Micropropagation. Sexual Reproduction 2. Pollination The process of transfer and deposition of pollen grains from the another to the stigmatic surface of the flower is called pollination. It is an essential event in the sexual reproduction of seed bearing plants.
Pollination is a pre-requisite for ensuring seed set and perpetuation of a species. Pollination is direct in Gymnosperms and indirect in Angiosperms. There are two main types of pollination - self pollination and cross pollination.
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