The techniques of plant cell culture facilitate the rapid production of variant cell lines via selection procedures similar to those employed in microbial systems. These variant cell lines are useful in research into the genetics and biochemistry of plant cells and in biotechnology for production of new plant varieties and secondary metabolites. We consider here some of the principles and problems associated with the selection of variant plant cells and the regeneration of plants with new characteristics. Later we see how the application of genetic engineering methods is now aiding this area of research. Plant cell selection has been performed with equal success using cells growing on solid media as calluses and in suspension as typical cell clumps. Rapidly growing, fine suspension cultures or friable calluses are generally the most suitable for selection purposes.
[...] Production of herbicide-tolerant plants Plant cell cultures have assumed an important role in the study of the mode of action of some herbicides. In addition there are now numerous examples where the techniques of in vitro selection and plant regeneration have been used to produce herbicide-resistant cells and plants. Production of new crop varieties in this way may have important applications in agriculture by allowing the effective control of weed species in a field without damage in the crop. Chaleff and Parsons (1978) selected cultured tobacco cells with tolerance of the herbicide picloram and then regenerated plants from four of the tolerant cell lines. [...]
[...] Such a mechanism of tolerance, whilst being very effective in cell culture, may be difficult to maintain in plants regenerated from the cells and indeed with glyphosate tolerant lines. Production of chill-tolerant plants from cultured cells There are a number of accounts of selection of cultured plant cells with enhanced tolerance of chilling, but descriptions of plants regenerated from such cells are rare. It seems likely that the lack of success in this area reflects the greater complexity of the physiological changes (e.g. [...]
[...] A variety of protocols has been used in order to isolate variant plant cells and the method of choice depends on the nature of the cell culture and the type of variant to be isolated. The selection procedures described here serve as examples only and do not form an exhaustive account of all the approaches employed. There have been many reports of selection of plant cell lines exhibiting auxotrophy or resistance to antimetabolites. Auxotrophic variants have not been so readily applied to research on plan improvement and are not considered here. [...]
[...] Variant plants regenerated in this way from selected cells must be analysed genetically in crossing experiments to determine the heritability of the new trait. This approach to the production of new variant plants, however, is sometimes hindered by failure of selected cells to regenerate plants or failure of regenerated plants to flower normally. Some 5-methyltryptophan- resistant Daucus carota cells, for example, were found to regenerate poorly. These cells contained anthranilate synthetase less sensitive to feedback inhibition by tryptophan and over-accumulated tryptophan and indole-3-acetic acid (IAA). [...]
[...] Demonstration of a true mutant may require crossing of plants regenerated from selected cell lines and analyses of progeny. Production of variant plants from selected cells Where it is possible to regenerate plants from variant cells selection techniques have potential for production of crop varieties with new characteristics some of which, eg. Herbicide and salt tolerance, may be desirable in field conditions. Some of the most thoroughly studied variant cell lines are those with resistances to amino acid analogues and antibiotics. [...]
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