Here is a compilation of essays on ‘Plant Tissue Culture’ for class 9, 10, 11 and 12. Find paragraphs, long and short essays on ‘Plant Tissue Culture’ especially written for school and college students.
Essay on Plant Tissue Culture
- Essay on the Meaning of Plant Tissue Culture
- Essay on the Medium of Plant Tissue Culture
- Essay on the Techniques of Plant Tissue Culture
- Essay on the Applications of Plant Tissue Culture
Essay # 1. Meaning of Plant Tissue Culture:
The scientific process by which cells, tissues or organs are developed in nutrient media to fulfil the demand, is called plant tissue culture.
The plant part taken out to be grown in a test-tube in special nutrient media is called explant. And the capacity of producing a whole plant from explant is called totipotency.
The nutrient media must provide a carbon source (such as sucrose), inorganic salts, vitamins, amino acids and growth regulators such as auxins, cytokinins, etc.
The production of a large number of plants in a short duration is practiced in floriculture and horticulture industry today, is known as micro-propagation. It is a technique of obtaining large number of plantlets by the tissue culture method.
The plants thus, generated are genetically similar to the original plant through which they are grown, so they are called somaclones. To recover healthy plants from diseased plants, meristem culture is practiced.
Meristem (axillary and apical) is the only virus-free part of virus-unaffected plant. Plants developed from meristem are banana, sugarcane, potato, etc.
Essay # 2. Medium of Plant Tissue Culture:
Tissue cultures can be done either in liquid medium or semi-solid medium. In liquid medium, plant material is immersed either partially or completely. On the other hand in semi-solid medium, plant material is placed on the surface of medium.
A balanced nutrient medium should fulfill the following requirements:
1. Inorganic Nutrients:
For normal growth of plants many inorganic nutrients like carbon, hydrogen, oxygen, nitrogen, calcium, potassium, phosphorus, sulphur, magnesium, iron, manganese, copper, boron, zinc, molybdenum are required. Some of them along with carbon, hydrogen and oxygen like nitrogen, calcium, potassium, phosphorus, sulphur and magnesium are required in large amount (concentration more than 0.05 m moll-1) and behave as macronutrients and others behave as micronutrients.
In White’s medium iron is added in the form of Fe (SO4)3, but in most of the nutrient media, iron is provided in the form of Fe EDTA. The supply of nitrogen is made by adding nitrates and ammonia. Nitrites cannot replace nitrates. Nitrites in low concentrations are ineffective but in higher concentrations have been found to be toxic. Ammonium salts give favourable results. EDTA (Ethylene diamine tetra acetic acid) behaves as chelating agent and is used to check iron from precipitating in solution.
2. Organic Nutrients:
Organic nutrients like amino acids and vitamins like thiamine (vitamin B1) are added to culture medium to get better results. Sucrose is added as a source of carbohydrate to provide carbon. Other sugars like glucose, fructose, maltose, mannose, lactose can also be used.
Some semisynthetic substances like coconut milk, yeast extract, tomato juice, malt extract, caesin hydrolysate etc. can also be added to promote growth of callus tissue. The effect of amino acids on growth of excised plant organs was studied by White (1932). Constabel (1958) used a mixture of 12 amino acids for the growth of jumpee tissue.
3. Growth Hormones:
Culture medium is supplemented with growth regulators like auxins, gibberellins and cytokinins. The commonly used auxins in tissue culture are Indole-3-acetic acid (IAA), lndole-3-butyric acid (IBA), Naphthalene acetic acid (NAA), Naphthoxy acetic acid, Parachlorophenoxy acetic acid (p-CPA), 2,4-dichlorophenoxy acetic acid (2,4-D) and 2,4,5-trichlorophenoxy acetic acid (2,4,5-T). Cytokinins are widely used for shoot differentiation, initiating the cell division etc. are Benzylamino purine (BAP), 2-Isopentenyl-adenine (2-ip) and Kinetin 6-furfuryl amino purine). GA3 is one of the most common gibberellins (out of 23) for its stimulating effect for development of plantlets.
The easier method for the preparation of culture media is to use the commercially available dry powder. The powder is dissolved in distilled water and sugar, desired supplements and agar are added. The final volume is made by adding water. The pH adjustment is made and medium is sterilized in autoclave.
Agar is used to solidify the medium. It is a polysaccharide obtained from seaweeds belonging to red algae. This is usually used at concentration of 0.8-1%. Higher concentration of agar makes the medium hard and diffusion of nutrients in plant tissues may be checked. Difco noble bacteriological agar is the purest form which is used for standard work.
The pH of medium is kept in between 5 to 5.8. This is adjusted by adding (0.1 N) NaOH or HCl. Higher pH makes the medium hard and low pH does not permit (satisfactory solidification.)
It is necessary to have complete aseptic conditions for and around culture apparatus, glassware, medium etc. to prevent the contamination of culture medium. Due to contamination in the medium microorganisms grow and ultimately they kill the plant tissue. The dimensions of sterilization room should be 6 × 6 × 4.5 sq. m. The room should have an autoclave. In case of non availability of autoclave, pressure cooker may also be used.
Sources of Contamination:
1. Microorganisms may be present in nutrient medium. To destroy them recommended pressure of 15 lb with temperature of 120°C autoclaving for 20 minutes should be done.
2. Plant tissue which is to be cultured must be surface sterilized before placing it on medium.
For this calcium or sodium hypochlorite solutions may be used. Mercuric chloride (1 to 2%) can also be used.
3. The inoculation chamber may be sterilized by UV radiations to kill the microorganisms.
Aeration of Culture:
Proper aeration is needed for the cultured plant. On semisolid medium plant tissue does not require particular attention for aeration (oxygen supply). However, in liquid medium, aeration is done by shaking the flasks on gyratory shaker with 80 to 220 rpm. Besides supplying oxygen to the plant part, shaking of the medium also brings about dissociation of the tissue into small clumps or even single cells.
Essay # 3. Techniques of Plant Tissue Culture :
1. Isolation of Plant Material:
The plant from which tissue is to be removed is called stock plant. Removed plant part or tissue (2 to 4 mm3 sterile segment) is known as explant. Explants may be pieces of stem, leaf, root, flower, and fruit of seed. Usually an explant containing morphologicaly uniform cells produces a relatively uniform type of callus and an explant which contains a variety of different cells types produces a mixed callus.
Tissue from young stem shows better results as compared to older stem which contains higher concentration of phenolic compounds. Inhibitory substances like coumarins, terpenoids etc. also retard the growth possibility in older plants. Usually, stem apex, seeds and other meristematic tissue is used to raise the callus tissue.
2. Cleaning of Glassware:
Most popular method employed for cleaning the glassware is to boil it in 10% sodium carbonate solution for 1-2 hours followed by through rinsing with tap water. The glassware is dipped in 30% HNO3, over night, then washed and rinsed with distilled water. Now glassware is dried and stored at a clean place. However, disposable sterile vessels can also be used.
3. Sterilization of Glassware Media and Plant Material:
Aseptic conditions for glassware medium is achieved in autoclave which helps to produce heat in the form of steam and increased pressure thus helping in killing the microorganisms. Glassware can also be sterilized in an oven by maintaining the temperature up to 160°C for atleast half an hour. However, culture media cannot be sterilized in oven because liquid would evaporate to dryness. Plant parts are also surface sterilized because they may also carry microorganisms with it.
Following technique is recommended to prepare the explant:
(a) Plant material may be picked up in the form of root tip, shoot tip, leaf tip, galls and seeds.
(b) From larger seeds, remove the seed coat and excise the embryo for culture.
(c) Surface sterilization can be done by sodium hypochlorite solution. Seeds may also be treated with 0.2% HgCl,
(d) After surface sterilization the flask containing the explant in the sterilized solution is transferred to sterile laminae airflow cabinet. The surface sterilized explants are removed and transferred to sterilized petridish with the help of sterile forceps. A specific part of explant is inoculated on sterilized medium.
Callus and Suspension Culture:
Callus is an unorganised mass of loosely arranged parenchymatous cells winch develop from parent tissue due to proliferation of cells.
Explant inoculated on sterilized medium or even isolated single cells from suspension cultures are capable of divisioris. Cells can proliferate and divide to form callus. Callus culture may be initiated from meristems. However, in grasses, callus culture is done from younger embryos. In cereals, seedling segments are used to produce callus.
Such cultures can be maintained for indefinite periods, if they are transferred regularly to fresh nutrient media at regular intervals. The process is called sub-culturing. Embryo culture is also used to form interspecific hybrid embryos which otherwise abort due to incompatibility between the embryo and maternal tissue.
When an explant is placed on the medium, cellular masses begin to appear around the cut edges of the explant. Surface of explant shows the signs of glistening, texture becomes rough. Explant divides and callus is formed within 2-3 weeks.
If the callus is to maintain for longer period, it should be divided into 2-4 segments. Each segment should be transferred to fresh culture medium (sub- culture technique). This is done because callus growth for longer period may lead to depletion of nutrients and desiccation of agar.
The steps may be summarized as:
Plant segment → sterilization → rinsing in water → Stem dies → plating → callus
Callus formation has been found in bryophytes, petridophytes and spermatophytes. Callus shows no organised meristems. Callus is an abnormal tissue which has the potential to form normal embryoid and roots, which further have the capacity to form plantlets.
However in suspension culture, single cell or small group of cells are suspended in liquid medium. Suspension cultures are agitated constantly at a speed of 100-250 rpm (revolutions per minute).
Agitation leads to:
(i) Proper aeration of culture.
(ii) Proper and constant mixing of culture medium.
(iii) Fragmentation of cell aggregates into still smaller groups of cells.
Following changes have been observed in various types of cultures:
(i) Biomass (cell/tissue dry matter) increases.
(ii) Nutrients in the culture medium decrease.
(iii) Medium volume decreases due to evaporation. To avoid the death of tissue cultures, cells/tissues are regularly shifted to new culture flasks having fresh nutrient media. This shifting to new vessels is called sub-culturing. It may however noticed that only small portion of culture is shifted to new culture vessel at the time of sub-culturing.
Meristem Culture (Fig. 9.20):
Pre-existing shoot meristems found in shoot tips, in the form of explants can also be used to produce shoots from them by meristem culture technique. Usually shoot tips and nodal segments are used as explants. Cytokinins like (BAP) are used in culture medium to promote the formation of axillary branches by overcoming the phenomenon of apical dominance. It leads to multiple shoot formation from each explant.
From this set of multiple shoots formed at the time of axillary branching, individual shoots are used as explant for culturing. If axillary branching does not occur, available shoot is cut into many small pieces at nodal regions and are used as explants for culturing. Shoots when attain the size of 2-3 cms are excised and rooted on suitable culture medium. After hardening, plants are established in field.
Uses of meristem culture are:
(i) For rapid clonal multiplication,
(ii) For production of virus free plants,
(iii) Used for germplasm conservation, and
(iv) Used for production of transgenic plants.
Embryogenesis mainly represents the process of embryo development. Somatic embryogenesis can be done by variety of explants e.g. stem, root, flower, bud, seed, embryo, nucellus, endosperm etc. Excision of young embryos from developing seeds and their development on culture medium is called embryo culture.
Practical applications of embryo culture:
1. In plants like Citrus, nucellus can be used for somatic embryogenesis. Embryogenic callus thus obtained can be used for many years because it retains its cellular totipotency for longer period. However in many plants nucellus degenerates at the time of formation of seed and cannot be used for somatic embryogenesis.
2. It is considered to be a rapid method for multiplication of many plants as compared to micropropagation.
3. Somatic embryogenesis can give rise to non- chemical mutants. Somatic embryos can be made to develop from single cell.
4. Virus free and non-pathogenic embryoids can develop from nucellus. This technique has been successfully employed in Citrus, as vegetative tissue is easily affected by viruses. Clones produced from nucellus have been found to be virus free.
5. Maternal embryos, haploid embryos and interspecific hybrid embryos can be made to develop by somatic embryogenesis. Such embryos usually abort due to non-availability of endosperm. Thus, this technique may prove helpful in various breeding programmes.
Objective of embryo culture:
It permits young embryos to for full development and finally able to form seedlings. However, older embryos can be easily and rapidly cultured than young embryos in vitro.
Essay # 4. Applications of Plant Tissue Culture:
(i) For rapid clonal multiplication.
(ii) For production of virus free plants.
(iii) Used for germ plasm conservation.
(iv) Used for production of transgenic plants.
Other techniques for improvement of varieties:
During mid 1970’s traditional methods of crop improvement like selection, breeding for yield, resistance to disease and drought were in practice. But by this time, new techniques like cell and protoplast culture, gene transfer etc. have also emerged.
Earlier cross breeding between many crop varieties and local hardy breeds made it possible to obtain cultivars that were more adapted and gave better results. The new plants produced by latest techniques are supposed to be resistant to diseases, predators and drought and even can be grown without fertilizer and pesticides.
Latest researches in the field of biotechnology are proving more useful in contributing to improved production and propagation of new cultivars which prove better in relation to nutritional quality, disease and salt resistance and other characters. With improvement of genetic engineering techniques, the time for generating and evaluating new germplasm can be drastically reduced. Chemical and biotechnological progresses have opened new frontiers to products of improved value from agricultural raw materials.
Biotechnology has been considered as the second phase of green revolution. Considerable research is in progress to increase the yield, improved fixation of nitrogen, increased nutritional quality and greater tolerance to salinity, alkalinity, acidity and other stresses.
Haploids produced through anther culture technique and their diplodization have lead to release of better varieties in many crops.
Some useful aspects of agricultural biotechnology are as under:
1. Improvement of nutritional quality.
2. Better nitrogen fixation.
3. Induction and selection of mutants, resistant to pathogens, adverse soil conditions, drought, salinity etc.
4. Production of disease resistant plants.
5. Micropropagation for biomass energy production.
Following methods are being used by agricultural bio-technologists for introducing the better characters in plants:
1. Somatic Cell Hybridization or Cytoplast or Cybird:
Somatic hybrids are formed when isolated naked protoplasts from two different varieties are fused. Process is called somatic hybridisation.
Power et.al. (1970) crossed oat with maize by this technique. Usually by protoplast fusion heterokaryon is formed, without the fusion of nuclei. One or both the nuclei may be lost later on. Sometimes one nucleus is left in the mixture of both the cytoplasms. This product is called Cytoplast or Cybird. The study of cybrids is proving useful for investigation of possible recombination within extrachromosomal genomes.
For example, protoplast of tomato is fused with that of potato and then they are grown to form new hybrid plants combining potato and tomato characteristics. It has resulted in the formation of pomato.
2. Somaclonal Variations:
Genetic variation present among plant cells of a culture is called somaclonal variation. The method refers to heritable changes which accumulate in callus from a somatic explant and express in the progendy of in-vitro regenerants obtained from callus. Somaclonal variations have been found to be taking place both for nuclear and cytoplasmic origin. The term somaclonal variation also represents the genetic variation present in plants regenerated from single culture.
3. Organ Culture Technique:
The technique is being used to culture isolated embryos. This is being done in those cases where viable zygotes are produced but due to incompatible gene interactions normal embryo and endosperm formation is checked.
4. Embryo Rescue:
Sometimes embryo formed in various crosses suffers from post-fertilization development inhibitory actions. Due to this normal viable seeds are not formed. Such hybrid embryos can be saved by growing them in artificial media.