28 July 2009

In vitro plant culture

The invention: Method for propagating plants in artificial media that has revolutionized agriculture. The people behind the invention: Georges Michel Morel (1916-1973), a French physiologist Philip Cleaver White (1913- ), an American chemist Plant Tissue Grows “In Glass” In the mid-1800’s, biologists began pondering whether a cell isolated from a multicellular organism could live separately if it were provided with the proper environment. In 1902, with this question in mind, the German plant physiologist Gottlieb Haberlandt attempted to culture (grow) isolated plant cells under sterile conditions on an artificial growth medium. Although his cultured cells never underwent cell division under these “in vitro” (in glass) conditions, Haberlandt is credited with originating the concept of cell culture. Subsequently, scientists attempted to culture plant tissues and organs rather than individual cells and tried to determine the medium components necessary for the growth of plant tissue in vitro. In 1934, Philip White grew the first organ culture, using tomato roots. The discovery of plant hormones, which are compounds that regulate growth and development, was crucial to the successful culture of plant tissues; in 1939, Roger Gautheret, P. Nobécourt, and White independently reported the successful culture of plant callus tissue. “Callus” is an irregular mass of dividing cells that often results from the wounding of plant tissue. Plant scientists were fascinated by the perpetual growth of such tissue in culture and spent years establishing optimal growth conditions and exploring the nutritional and hormonal requirements of plant tissue. Plants by the Millions A lull in botanical research occurred during World War II, but immediately afterward there was a resurgence of interest in applying tissue culture techniques to plant research. Georges Morel, a plant physiologist at the National Institute for Agronomic Research in France, was one of many scientists during this time who had become interested in the formation of tumors in plants as well as in studying various pathogens such as fungi and viruses that cause plant disease. To further these studies, Morel adapted existing techniques in order to grow tissue from a wider variety of plant types in culture, and he continued to try to identify factors that affected the normal growth and development of plants. Morel was successful in culturing tissue from ferns and was the first to culture monocot plants. Monocots have certain features that distinguish them fromthe other classes of seed-bearing plants, especially with respect to seed structure. More important, the monocots include the economically important species of grasses (the major plants of range and pasture) and cereals. For these cultures, Morel utilized a small piece of the growing tip of a plant shoot (the shoot apex) as the starting tissue material. This tissue was placed in a glass tube, supplied with a medium containing specific nutrients, vitamins, and plant hormones, and allowed to grow in the light. Under these conditions, the apex tissue grew roots and buds and eventually developed into a complete plant. Morel was able to generate whole plants from pieces of the shoot apex that were only 100 to 250 micrometers in length. Morel also investigated the growth of parasites such as fungi and viruses in dual culture with host-plant tissue. Using results from these studies and culture techniques that he had mastered, Morel and his colleague Claude Martin regenerated virus-free plants from tissue that had been taken from virally infected plants. Tissues from certain tropical species, dahlias, and potato plants were used for the original experiments, but after Morel adapted the methods for the generation of virus-free orchids, plants that had previously been difficult to propagate by any means, the true significance of his work was recognized. Morel was the first to recognize the potential of the in vitro culture methods for the mass propagation of plants. He estimated that several million plants could be obtained in one year from a single small piece of shoot-apex tissue. Plants generated in this manner were clonal (genetically identical organisms prepared from a single plant).With other methods of plant propagation, there is often a great variation in the traits of the plants produced, but as a result of Morel’s ideas, breeders could select for some desirable trait in a particular plant and then produce multiple clonal plants, all of which expressed the desired trait. The methodology also allowed for the production of virus-free plant material, which minimized both the spread of potential pathogens during shipping and losses caused by disease. Consequences Variations on Morel’s methods are used to propagate plants used for human food consumption; plants that are sources of fiber, oil, and livestock feed; forest trees; and plants used in landscaping and in the floral industry. In vitro stocks are preserved under deepfreeze conditions, and disease-free plants can be proliferated quickly at any time of the year after shipping or storage. The in vitro multiplication of plants has been especially useful for species such as coconut and certain palms that cannot be propagated by other methods, such as by sowing seeds or grafting, and has also become important in the preservation and propagation of rare plant species that might otherwise have become extinct. Many of these plants are sources of pharmaceuticals, oils, fragrances, and other valuable products. The capability of regenerating plants from tissue culture has also been crucial in basic scientific research. Plant cells grown in culture can be studied more easily than can intact plants, and scientists have gained an in-depth understanding of plant physiology and biochemistry by using this method. This information and the methods of Morel and others have made possible the genetic engineering and propagation of crop plants that are resistant to disease or disastrous environmental conditions such as drought and freezing. In vitro techniques have truly revolutionized agriculture.

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