Cell culture: Plant cells
Culturing Plant Cells (Genetics & Inherited Conditions)
Plant cell cultures are typically initiated by taking explants—such as root, stem, leaf, or flower tissue—from an intact plant. These explants are surface-sterilized and then placed in vitro on a formulated, artificial growth medium containing various inorganic salts, a carbon source (such as sucrose), vitamins, and various plant growth regulators, depending on the desired outcome. There are many commercially available media formulations; the two most common include MS (murashige and skoog) and WPM (woody plant media). Alternatively, customized formulations may be necessary for culturing certain plant species. One of the most important uses of plant tissue culture has been for the mass propagation of economically important agricultural and horticultural crops. Since the 1980’s, however, plant cell culture has become an important tool allowing for direct genetic manipulations of several important agricultural crops, including corn, soybeans, potatoes, cotton, and canola, to name only a few.
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Appearance in Culture (Genetics & Inherited Conditions)
The underlying basis for the prevalent and continued use of plant cell culture is the remarkable totipotent ability of plant cells and tissues. They are able to dedifferentiate in culture, essentially becoming a nondifferentiated clump of meristematic, loosely connected cells termed callus. Callus tissue can be systematically subcultured and then, depending on exposure to various plant growth regulators incorporated in the growth media, induced to undergo morphogenesis. Morphogenesis refers to the redifferentiation of callus tissue to form specific plant organs, such as roots, shoots, or subsequent whole plants. Many plant species can also be manipulated in culture to form somatic embryos, which are asexual embryoid structures that can then develop into plantlets. The totipotency of plant cells thus allows for a single cell, such as a plant protoplast, to be able to regenerate into a complete, whole plant. An analogous comparison of the totipotency of plant cells would be that of stem cells in animals. Genetic manipulation of individual plant cells coupled with their totipotency makes plant cell culture a powerful tool for the plant geneticist.
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Role of Plant Growth Regulators (Genetics & Inherited Conditions)
Hormones or plant growth regulators (PGRs) are naturally occurring or synthetic compounds that, in small concentrations, have tremendous regulatory influence on the physiological and morphological growth and development of plants. There are several established classes of PGRs, including auxins, cytokinins, gibberellins, abscisic acid (ABA), and ethylene. Additionally, several other compounds, such as polyamines, oligosaccharides, and sterols, exert hormonelike activity in plant cell cultures. While each class has a demonstrative and unique effect on overall whole plant growth and development, auxins and cytokinins continue to be the most widely used in manipulating plant growth in vitro. Auxins (such as IAA, NAA, and 2,4-D) and cytokinins (such as zeatin, kinetin, and BAP) are frequently used in combination in plant tissue culture. Generally, a high auxin-to-cytokinin ratio results in the induction of root tissue from callus, while a high cytokinin-to-auxin ratio results in the induction of shoot formation. For many plant species, an intermediate ratio of auxin to cytokinin results in continued callus formation.
There are also specific uses of certain PGRs in plant cell culture. For example, 2,4-D is typically used to induce somatic embryogenesis in cultures but then must be removed for subsequent embryoid development. Gibberellins, such as GA4 and GA7, can be inhibitory to morphogenesis. Some PGRs may even...
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Applications and Potential (Genetics & Inherited Conditions)
Plant cell culture as a tool has greatly enhanced the ability of the plant geneticist in the area of crop improvement. Haploid cell cultures initiated from pollen can result in homozygous whole plants, which are very useful as pure lines in breeding programs. In such plants, recessive mutations are easily identified.
The enzymatic removal of the plant cell wall yields naked plant protoplasts, which are more amenable to genetic manipulation. Protoplasts of different species can be chemically or electrically fused to give somatic hybrids that may not be obtained through traditional sexual crossing due to various types of sexual incompatibility. As they divide and regenerate cell walls, these somatic hybrids can then be selected for desired agriculture characteristics, such as insect or disease resistance.
The isolation of plant protoplasts from leaves results in millions of individual cells. As they divide, grow, and differentiate into whole plants, some may contain spontaneous mutations or other changes which can be selected for. Screening for such characteristics, such as salt tolerance or disease resistance, can be done in vitro, thereby saving time and space.
Another use of plant cell culture in crop improvement involves directed genetic transformation. Genes from other species, including bacteria, animals, and other plants, have been introduced into cell cultures, resulting in genetically modified...
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Further Reading (Genetics & Inherited Conditions)
George, Edwin F., Michael A. Hall, and Geert-Jan De Klerk, eds. Plant Propagation by Tissue Culture. 3d ed. 2 vols. London: Springer, 2008. An exhaustive presentation of nutritional media components and discussion of PGR effects in culture. Provides specifics on the culture of several hundred species. Illustrations, photographs.
Neumann, Karl-Hermann Neumann, Ashwani Kumar, and Jafargholi Imani. Plant Cell and Tissue Culture—a Tool in Biotechnology: Basics and Application. Berlin: Springer, 2009. An introduction to the field of plant cell and tissue culture, including a detailed description of various techniques employed in laboratories worldwide, an account of applications in plant propagation and gene technology, and a survey of advances in the field.
Razdan, M. K. Introduction to Plant Tissue Culture. 2d ed. Enfield, N.H.: Science, 2003. Provides an introductory overview of plant tissue culture, including information about its history, basic aspects, and applications to plant breeding, horticulture, and forestry.
Trigiano, Robert, and Dennis Gray, eds. Plant Development and Biotechnology. Boca Raton, Fla.: CRC Press, 2005. Includes a history of plant tissue and cell culture, descriptions of various methods of plant cell culture, and discussions of plant propagation and development concepts and crop improvement techniques. Designed for employees in tissue culture research...
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Web Sites of Interest (Genetics & Inherited Conditions)
Plant Tissue Culture. http://www.liv.ac.uk/~sd21/tisscult/introduction.htm. Prepared by the School of Biological Sciences at the University of Liverpool, this site provides an introduction to plant cell culture, describing what it is and its uses; three illustrated case studies; and a bibliography.
Plant Tissue Culture Exchange. http://aggie-horticulture.tamu.edu/tisscult. Texas A&M University maintains this Web site, which contains case studies, articles, resources, and other information about plant tissue culture.
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