Cell culture of plant cells
Cell culture of plant cells is the process of growing and maintaining various plant cells, tissues, or organs in a controlled artificial environment, typically utilizing a nutrient-rich medium supplemented with plant growth regulators. This technique is invaluable for plant geneticists and has applications ranging from fundamental research on plant development to the enhancement of economically significant agricultural species. The process often begins with the collection of explants—like roots, stems, or leaves—followed by surface sterilization and placement on a specialized growth medium, such as Murashige and Skoog (MS) or Woody Plant Medium (WPM).
One of the key characteristics of plant cells is their totipotency, which allows them to revert to a meristematic state and form undifferentiated tissue known as callus. This callus can then be stimulated to differentiate into specific organs or even whole plants through the strategic use of plant growth regulators. These regulators, including auxins and cytokinins, significantly influence plant growth and can be manipulated to achieve desired outcomes.
Plant cell culture is also pivotal in crop improvement, enabling the creation of haploid plants and facilitating genetic engineering through techniques such as Agrobacterium-mediated transformation. As researchers confront challenges like climate change and water scarcity, plant cell culture remains a promising avenue for producing enhanced plants with beneficial traits. However, the practice of genetic modification raises important discussions about food safety and biodiversity.
Cell culture of plant cells
SIGNIFICANCE: Plant cell culture is the establishment and subsequent growth of various plant cells, tissues, or organs in vitro, using an artificial nutritional medium usually supplemented by various plant growth regulators. It has become a tool that plant geneticists use for purposes ranging from the basic study of plant development to the genetic improvement of economically important agricultural plant species.
Culturing Plant Cells
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 are 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 1980s, 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.
Appearance in Culture
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 make the plant cell culture a powerful tool for the plant geneticist.
Role of Plant Growth Regulators
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 hormone-like 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 elicit opposite morphogenic effects in two different plant species. Nevertheless, the use of PGRs remains essential in plant cell culture to direct morphological development.
Applications and Potential
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 (GM) plants. The most common technique used to transfer desired genes uses the bacterium Agrobacterium tumefaciens. Other techniques include electroporation, microinjection, and particle bombardment with “gene guns.” As genetic engineering of plants proceeds and is refined, plant cell culture will continue to play a vital role as a tool in this effort.
Plant-based products are important in many commercial applications. Among these are cosmetics, medicines, and food products. However, meeting demand often proves difficult, expecially when faced with challenges such as shortage of fresh water, global climate change, and the need to produce food. Plant cell culture is one area in which researchers are seeking solutions to these problems.
One of the solutions being researched is genetically altering the genes responsible for plant cell differentiation. Those involved with this approach have promoted it as a simpler and less expensive way to grow plants with the most desirable qualities. However, the practice of genetically modifying plants, especially those used for food, has raised concerns about the effects on humans and animals that consume genetically altered crops as well as the practice's potential negative effects on biodiversity.
Key Terms
- callusa group of undifferentiated plant cells growing in a clump
- morphogenesisthe induction and formation of organized plant parts or organs
- plant growth regulatorshormone-like substances that profoundly affect plant growth and development
- somatic embryosasexual embryoid structures derived from somatic cells
- totipotencythe ability of a plant cell or part to regenerate into a whole plant
Bibliography
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