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Plant biotechnology

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Growing conditions, plant protection

Although modern biotechnology is based on advances in molecular genetics and recombinant DNA technology, exploitation of these advances in plants has been facilitated by two other established techniques in plant physiology. They are the culture of tissue, cells, and protoplasts and the technique of protoplast fusion.
Tissue culture is the technique of maintaining plant tissues indefinitely on an artificial medium. It has long been exploited as a system for the study of cell division, enlargement, and differentiation in laboratories around the world.
Although plant tissue culture is most often carried out on solid medium, containing agar, tissues can also be cultured in liquid medium (for example somatic embryo culture). With a relatively small investment in space, technical support, and materials, tissue culture has made it possible to produce literally millions of high-quality, genetically uniform plants. Tissue culture is very useful for: • in vitro production of secondary metabolites, • in vitro propagation (cryopreservation, culture systems, elicitors, growth regulators) • in vitro, somaclonal and gametoclonal selection, • bioreactors (cell suspension cultures, hairy root cultures, stirred tank bioreactors), • cell, tissue and embryomanipulation (embryo rescue, haploid production, somatic embryogenesis), • microspore and macrospore culture (anther and pollen culture).

Protoplasts are plant cells that have had their cell walls removed by digestion with the enzyme cellulase and other cell wall-degrading enzymes. Protoplasts can be isolated from virtually any plant tissue and, in many cases, remain capable of sustained cell division. As with tissue culture, cells regenerated from protoplasts can be induced to divide and form callus and, eventually, to regenerate fertile plants. Species that have been fully regenerated from protoplasts include potato, tobacco, pepper and tomato.
Removal of the constraints imposed by the cell wall has stimulated many fundamental studies on plant cell biology. Perhaps most significant is the capacity of protoplast to fuse, giving rise to somatic hybrids. This allows hybrids to be formed between species that are genetically incompatible. Moreover, plants have cytoplasmic genomes that are maternally inherited. Some of these genes have practical as well as theoretical importance. Protoplast fusion makes it possible to produce new cytoplasmic-nuclear combinations without the time-consuming and expensive backcrossing required by conventional breeding.
Finally, and perhaps most importantly, the absence of a cell wall facilitates the genetic transformation of plants by the direct transfer of genes into protoplasts. Plants that are subsequently regenerated will be transformed and express the new gene or genes.