Micropropagation: A Widely Used Technique

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Micropropagation has become a widely used technique for the large-scale and rapid propagation plants. Over the last 30 years, great strides have been made to develop and optimize micropropagation methods and culture media for the large-scale multiplication of a large number of plant species. However, despite the improved propagation efficiency, the method is still plagued with many problems, which limit in certain cases the profitability of the technique. Indeed, in vitro plantlets present many aberrations like, stomatal malfunction, poor epicuticular wax deposition, somaclonal variation, poor rooting, and hyperhydricity. Many species cannot be cost-effectively propagated by tissue culture due to these induced anatomical and physiological modifications (which lead to an excessive loss during hardening). These developmental problems stem from the particular conditions plants are cultured under. Indeed, the in vitro culture environment is typically characterized by low lighting, poor gas exchanges, high relative humidity and high mineral and sugar contents. Yet, even if plantlets are provided with all essential trophic elements, and are cultured under constant temperature and light, they still appear to suffer from many types of stress.
Over the years, sugar has been considered an essential component of the plant in vitro culture medium. However, in addition to its nutritional role, sugar regulates many important metabolic processes associated with plant growth and development (signalling functions). At the cellular level, sugars are essential for intermediary and respiratory metabolism and are the substrate for the synthesis of complex carbohydrates such as starch and cellulose. In addition, sugars supply the precursors for amino a...

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...e to understand the plant physiology by gaining a more global picture of the biochemical composition. In a seminal work, Roessner et al. (2000) used GC-MS to obtain a comprehensive metabolic profile of a singles extracts of soil or in vitro grown potato tubers. About 77 metabolites of various biochemical groups were detected and quantified at once. This analytical method proved to be powerful and allowed the simultaneous analysis of a large set of metabolite and revealed major differences between the tubers from different origin. Using the same technique, Jeong et al. (2004) showed that 64 metabolites accumulated differentially during the transition from sink to source of quacking aspen leaves two-thirds of which showed more than 4-fold changes in relative abundance. In this case, the metabolic profiling of three leaf stages yielded distinct biochemical phenotypes.

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