Micropropagation

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Simple micropropagation technique.svg
A rose plant that began as cells grown in a tissue culture Rose grown from tissue culture.jpg
A rose plant that began as cells grown in a tissue culture

Micropropagation or tissue culture is the practice of rapidly multiplying plant stock material to produce many progeny plants, using modern plant tissue culture methods. [1]

Contents

Micropropagation is used to multiply a wide variety of plants, such as those that have been genetically modified or bred through conventional plant breeding methods. It is also used to provide a sufficient number of plantlets for planting from seedless plants, plants that do not respond well to vegetative reproduction or where micropropagation is the cheaper means of propagating (e.g. Orchids [2] ). Cornell University botanist Frederick Campion Steward discovered and pioneered micropropagation and plant tissue culture in the late 1950s and early 1960s. [3]

Steps

In short, steps of micropropagation can be divided into four stages:

  1. Selection of mother plant
  2. Multiplication
  3. Rooting and acclimatizing
  4. Transfer new plant to soil

Selection of mother plant

In vitro culture of plants in a controlled, sterile environment Culture in vitro.JPG
In vitro culture of plants in a controlled, sterile environment

Micropropagation begins with the selection of plant material to be propagated. The plant tissues are removed from an intact plant in a sterile condition. Clean stock materials that are free of viruses and fungi are important in the production of the healthiest plants. Once the plant material is chosen for culture, the collection of explant(s) begins and is dependent on the type of tissue to be used, including stem tips, anthers, petals, pollen and other plant tissues. The explant material is then surface sterilized, usually in multiple courses of bleach and alcohol washes, and finally rinsed in sterilized water. This small portion of plant tissue, sometimes only a single cell, is placed on a growth medium, typically containing Macro and micronutrients, water, sucrose as an energy source and one or more plant growth regulators (plant hormones). Usually, the medium is thickened with a gelling agent, such as agar, to create a gel which supports the explant during growth. Some plants are easily grown on simple media, but others require more complicated media for successful growth; the plant tissue grows and differentiates into new tissues depending on the medium. For example, media containing cytokinin are used to create branched shoots from plant buds.

Multiplication

Multiplication is the taking of tissue samples produced during the first stage and increasing their number. Following the successful introduction and growth of plant tissue, the establishment stage is followed by multiplication. Through repeated cycles of this process, a single explant sample may be increased from one to hundreds and thousands of plants. Depending on the type of tissue grown, multiplication can involve different methods and media. If the plant material grown is callus tissue, it can be placed in a blender and cut into smaller pieces and recultured on the same type of culture medium to grow more callus tissue. If the tissue is grown as small plants called plantlets, hormones are often added that cause the plantlets to produce many small offshoots. After the formation of multiple shoots, these shoots are transferred to rooting medium with a high auxin\cytokinin ratio. After the development of roots, plantlets can be used for hardening.

Pretransplant

Banana plantlets transferred to soil (with vermicompost) from plant media. This process is done for acclimatization of plantlets to the soil as they were previously grown in plant media. After growing for some days the plantlets are transferred to the field. Banana plantlets transferred to soil (with vermicompost) from plant media.jpg
Banana plantlets transferred to soil (with vermicompost) from plant media. This process is done for acclimatization of plantlets to the soil as they were previously grown in plant media. After growing for some days the plantlets are transferred to the field.

This stage involves treating the plantlets/shoots produced to encourage root growth and "hardening." It is performed in vitro , or in a sterile "test tube" environment.

"Hardening" refers to the preparation of the plants for a natural growth environment. Until this stage, the plantlets have been grown in "ideal" conditions, designed to encourage rapid growth. Due to the controlled nature of their maturation, the plantlets often do not have fully functional dermal coverings. This causes them to be highly susceptible to disease and inefficient in their use of water and energy. In vitro conditions are high in humidity, and plants grown under these conditions often do not form a working cuticle and stomata that keep the plant from drying out. When taken out of culture, the plantlets need time to adjust to more natural environmental conditions. Hardening typically involves slowly weaning the plantlets from a high-humidity, low light, warm environment to what would be considered a normal growth environment for the species in question.

Transfer from culture

Plant tissue cultures being grown at a USDA seed bank, the National Center for Genetic Resources Preservation Plant tissue cultures, National Center for Genetic Resources Preservation, USDA.jpg
Plant tissue cultures being grown at a USDA seed bank, the National Center for Genetic Resources Preservation

In the final stage of plant micropropagation, the plantlets are removed from the plant media and transferred to soil or (more commonly) potting compost for continued growth by conventional methods.

This stage is often combined with the "pretransplant" stage.

Methods

There are many methods of plant micro propagation.

Meristem culture

In Meristem culture, the meristem and a few subtending leaf primordia are placed into a suitable growing media. where they are induced to form new meristem. These meristems are then divided and further grown and multiplied. To produce plantlets the meristems are taken of from their proliferation medium and put on a regeneration medium. When an elongated rooted plantlet is produced after some weeks, it can be transferred to the soil. A disease-free plant can be produced by this method. Experimental result also suggest that this technique can be successfully utilized for rapid multiplication of various plant species, e.g. Coconut, [4] strawberry, [5] sugarcane. [6]

Callus culture

A callus is mass of undifferentiated parenchymatous cells. When a living plant tissue is placed in an artificial growing medium with other conditions favorable, callus is formed. The growth of callus varies with the homogenous levels of auxin and cytokinin and can be manipulated by endogenous supply of these growth regulators in the culture medium. The callus growth and its organogenesis or embryogenesis can be referred into three different stages.

Embryo culture

In embryo culture, the embryo is excised and placed into a culture medium with proper nutrient in aseptic condition. To obtain a quick and optimum growth into plantlets, it is transferred to soil. It is particularly important for the production of interspecific and intergeneric hybrids and to overcome the embryo.

Protoplast culture

In protoplast culture, the plant cell can be isolated with the help of wall degrading enzymes and growth in a suitable culture medium in a controlled condition for regeneration of plantlets. Under suitable conditions the protoplast develops a cell wall followed by an increase in cell division and differentiation and grows into a new plant. The protoplast is first cultured in liquid medium at 25 to 28 C with a light intensity of 100 to 500 lux or in dark and after undergoing substantial cell division, they are transferred into solid medium congenial or morphogenesis in many horticultural crops respond well to protoplast culture.

Advantages

Micropropagation has a number of advantages over traditional plant propagation techniques:

Disadvantages

Micropropagation is not always the perfect means of multiplying plants. Conditions that limits its use include:

The major limitation in the use of micropropagation for many plants is the cost of production; for many plants the use of seeds, which are normally disease free and produced in good numbers, readily produce plants (see orthodox seed) in good numbers at a lower cost. For this reason, many plant breeders do not utilize micropropagation because the cost is prohibitive. Other breeders use it to produce stock plants that are then used for seed multiplication.

Mechanisation of the process could reduce labour costs, but has proven difficult to achieve, despite active attempts to develop technological solutions.

Applications

Micropropagation facilitates the growth, storage, and maintenance of a large number of plants in small spaces which makes it a cost-effective process. Micropropagation is used for germplasm storage and the protection of endangered species.

Related Research Articles

<i>Canna</i> (plant) Genus of flowering plants in the family Cannaceae

Canna or canna lily is the only genus of flowering plants in the family Cannaceae, consisting of 10 species. All of the genus's species are native to the American tropics and naturalized in Europe, India and Africa in the 1860s. Although they grow native to the tropics, most cultivars have been developed in temperate climates and are easy to grow in most countries of the world, as long as they receive at least 6–8 hours average sunlight during the summer, and are moved to a warm location for the winter. See the Canna cultivar gallery for photographs of Canna cultivars.

<span class="mw-page-title-main">Meristem</span> Type of plant tissue involved in cell proliferation

The meristem is a type of tissue found in plants. It consists of undifferentiated cells capable of cell division. Cells in the meristem can develop into all the other tissues and organs that occur in plants. These cells continue to divide until a time when they get differentiated and then lose the ability to divide.

<span class="mw-page-title-main">Plant hormone</span> Chemical compounds that regulate plant growth and development

Plant hormones are signal molecules, produced within plants, that occur in extremely low concentrations. Plant hormones control all aspects of plant growth and development, including embryogenesis, the regulation of organ size, pathogen defense, stress tolerance and reproductive development. Unlike in animals each plant cell is capable of producing hormones. Went and Thimann coined the term "phytohormone" and used it in the title of their 1937 book.

<span class="mw-page-title-main">Vegetative reproduction</span> Asexual method of reproduction in plants

Vegetative reproduction is any form of asexual reproduction occurring in plants in which a new plant grows from a fragment or cutting of the parent plant or specialized reproductive structures, which are sometimes called vegetative propagules.

<span class="mw-page-title-main">Tissue culture</span> Growth of tissues or cells in an artificial medium separate from the parent organism

Tissue culture is the growth of tissues or cells in an artificial medium separate from the parent organism. This technique is also called micropropagation. This is typically facilitated via use of a liquid, semi-solid, or solid growth medium, such as broth or agar. Tissue culture commonly refers to the culture of animal cells and tissues, with the more specific term plant tissue culture being used for plants. The term "tissue culture" was coined by American pathologist Montrose Thomas Burrows. This is possible only in certain conditions. It also requires more attention. It can be done only in genetic labs with various chemicals.

<span class="mw-page-title-main">Protoplast</span> Cell stripped of cell-wall

Protoplast, is a biological term coined by Hanstein in 1880 to refer to the entire cell, excluding the cell wall. Protoplasts can be generated by stripping the cell wall from plant, bacterial, or fungal cells by mechanical, chemical or enzymatic means.

<span class="mw-page-title-main">Callus (cell biology)</span> Growing mass of unorganized plant parenchyma cells

Plant callus is a growing mass of unorganized plant parenchyma cells. In living plants, callus cells are those cells that cover a plant wound. In biological research and biotechnology callus formation is induced from plant tissue samples (explants) after surface sterilization and plating onto tissue culture medium in vitro. The culture medium is supplemented with plant growth regulators, such as auxin, cytokinin, and gibberellin, to initiate callus formation or somatic embryogenesis. Callus initiation has been described for all major groups of land plants.

Plant embryonic development, also plant embryogenesis is a process that occurs after the fertilization of an ovule to produce a fully developed plant embryo. This is a pertinent stage in the plant life cycle that is followed by dormancy and germination. The zygote produced after fertilization must undergo various cellular divisions and differentiations to become a mature embryo. An end stage embryo has five major components including the shoot apical meristem, hypocotyl, root meristem, root cap, and cotyledons. Unlike the embryonic development in animals, and specifically in humans, plant embryonic development results in an immature form of the plant, lacking most structures like leaves, stems, and reproductive structures. However, both plants and animals including humans, pass through a phylotypic stage that evolved independently and that causes a developmental constraint limiting morphological diversification.

Kinetin (/'kaɪnɪtɪn/) is a cytokinin-like synthetic plant hormone that promotes cell division in plants. Kinetin was originally isolated by Carlos O. Miller and Skoog et al. as a compound from autoclaved herring sperm DNA that had cell division-promoting activity. It was given the name kinetin because of its ability to induce cell division, provided that auxin was present in the medium. Kinetin is often used in plant tissue culture to induce callus formation and regenerate shoot tissues from callus.

<span class="mw-page-title-main">Indole-3-butyric acid</span> Chemical compound

Indole-3-butyric acid (1H-indole-3-butanoic acid, IBA) is a white to light-yellow crystalline solid, with the molecular formula C12H13NO2. It melts at 125 °C in atmospheric pressure and decomposes before boiling. IBA is a plant hormone in the auxin family and is an ingredient in many commercial horticultural plant rooting products.

In biology, explant culture is a technique to organotypically culture cells from a piece or pieces of tissue or organ removed from a plant or animal. The term explant can be applied to samples obtained from any part of the organism. The extraction process is extensively sterilized, and the culture can be typically used for two to three weeks.

Important structures in plant development are buds, shoots, roots, leaves, and flowers; plants produce these tissues and structures throughout their life from meristems located at the tips of organs, or between mature tissues. Thus, a living plant always has embryonic tissues. By contrast, an animal embryo will very early produce all of the body parts that it will ever have in its life. When the animal is born, it has all its body parts and from that point will only grow larger and more mature. However, both plants and animals pass through a phylotypic stage that evolved independently and that causes a developmental constraint limiting morphological diversification.

<span class="mw-page-title-main">Somatic fusion</span> Genetic modification fusing plants into a hybrid

Somatic fusion, also called protoplast fusion, is a type of genetic modification in plants by which two distinct species of plants are fused together to form a new hybrid plant with the characteristics of both, a somatic hybrid. Hybrids have been produced either between different varieties of the same species or between two different species.

<span class="mw-page-title-main">Plant tissue culture</span> Growing cells under lab conditions

Plant tissue culture is a collection of techniques used to maintain or grow plant cells, tissues, or organs under sterile conditions on a nutrient culture medium of known composition. It is widely used to produce clones of a plant in a method known as micropropagation. Different techniques in plant tissue culture may offer certain advantages over traditional methods of propagation, including:

<i>Dracaena pinguicula</i> Species of flowering plant

Dracaena pinguicula, synonym Sansevieria pinguicula, also known as the walking sansevieria, is a xerophytic CAM succulent native to the Bura area of Kenya, near Garissa. The species was described by Peter René Oscar Bally in 1943.

Embryo rescue is one of the earliest and successful forms of in-vitro culture techniques that is used to assist in the development of plant embryos that might not survive to become viable plants. Embryo rescue plays an important role in modern plant breeding, allowing the development of many interspecific and intergeneric food and ornamental plant crop hybrids. This technique nurtures the immature or weak embryo, thus allowing it the chance to survive. Plant embryos are multicellular structures that have the potential to develop into a new plant. The most widely used embryo rescue procedure is referred to as embryo culture, and involves excising plant embryos and placing them onto media culture. Embryo rescue is most often used to create interspecific and intergeneric crosses that would normally produce seeds which are aborted. Interspecific incompatibility in plants can occur for many reasons, but most often embryo abortion occurs In plant breeding, wide hybridization crosses can result in small shrunken seeds which indicate that fertilization has occurred, however the seed fails to develop. Many times, remote hybridizations will fail to undergo normal sexual reproduction, thus embryo rescue can assist in circumventing this problem.

Hyperhydricity is a physiological malformation that results in excessive hydration, low lignification, impaired stomatal function and reduced mechanical strength of tissue culture-generated plants. The consequence is poor regeneration of such plants without intensive greenhouse acclimation for outdoor growth. Additionally, it may also lead to leaf-tip and bud necrosis in some cases, which often leads to loss of apical dominance in the shoots. In general, the main symptom of hyperhydricity is translucent characteristics signified by a shortage of chlorophyll and high water content. Specifically, the presence of a thin or absent cuticular layer, reduced number of palisade cells, irregular stomata, less developed cell wall and large intracellular spaces in the mesophyll cell layer have been described as some of the anatomic changes associated with hyperhydricity.

<span class="mw-page-title-main">Somatic embryogenesis</span> Method to derive a plant or embryo from a single somatic cell

Somatic embryogenesis is an artificial process in which a plant or embryo is derived from a single somatic cell. Somatic embryos are formed from plant cells that are not normally involved in the development of embryos, i.e. ordinary plant tissue. No endosperm or seed coat is formed around a somatic embryo.

Photoautotrophic tissue culture is defined as "micropropagation without sugar in the culture medium, in which the growth or accumulation of carbohydrates of cultures is dependent fully upon photosynthesis and inorganic nutrient uptake".

Ernest Aubrey Ball was an American professor of botany and a pioneer of meristem culture.

References

  1. "Micropropagation - Definitions from Dictionary.com". dictionary.reference.com. Retrieved 2008-03-17.
  2. Chugh, Samira; Guha, Satyakam; Rao, I. Usha (2009-11-03). "Micropropagation of orchids: A review on the potential of different explants". Scientia Horticulturae. 122 (4): 507–520. doi:10.1016/j.scienta.2009.07.016. ISSN   0304-4238.
  3. "Frederick Campion Steward" (PDF). Cornell University Faculty Memorial Statement. Archived from the original (PDF) on 2012-04-02.
  4. Wilms, Hannes; De Bièvre, Dries; Longin, Kevin; Swennen, Rony; Rhee, Juhee; Panis, Bart (2021-09-15). "Development of the first axillary in vitro shoot multiplication protocol for coconut palms". Scientific Reports. 11 (1): 18367. Bibcode:2021NatSR..1118367W. doi:10.1038/s41598-021-97718-1. ISSN   2045-2322. PMC   8443624 . PMID   34526563.
  5. Naing, Aung Htay; Kim, Si Hyun; Chung, Mi Young; Park, Soon Ki; Kim, Chang Kil (2019-04-13). "In vitro propagation method for production of morphologically and genetically stable plants of different strawberry cultivars". Plant Methods. 15 (1): 36. doi: 10.1186/s13007-019-0421-0 . ISSN   1746-4811. PMC   6461810 . PMID   31011361.
  6. Salokhe, Shubhangi (2021-06-01). "Development of an efficient protocol for production of healthy sugarcane seed cane through Meristem culture". Journal of Agriculture and Food Research. 4: 100126. doi: 10.1016/j.jafr.2021.100126 . ISSN   2666-1543. S2CID   233618279.
  7. Maciej Hempel, М. Хемпел & М. Хемпел (1986) Some Economical Aspects of Commercial Micropropagation, Biotechnology & Bioindustry, 1:5, 22-26, DOI: 10.1080/02052067.1986.10824247