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Plant cell and tissue cultures originated from basic studies where they serve as model systems for many areas of research in botany, dealing mainly with growth and differentiation. A short summary shall indicate possibilities of practical use of these systems, which to date have only been little exploited.

One area of application broadly used is the propagation of plants. Commercially, this is currently certainly the most important application of cell and tissue culture systems (Fig. 1.1). Most prominent are meristem cultures in broadest terms, first used for the propagation of orchids (Morel 1963, 1974), and later for other ornamental plants (Chap. 7). During recent years, methods were developed also for the propagation of woody plants of importance for recultivation of forest areas, e.g., affected by “acid rain”. Cell culture techniques will always be applied to propagate highly valuable single plants not suitable for cloning by cuttings, due to morphological and/or anatomical constraints. Propagation by meristem culture will also be employed to produce virus-free plants from infected mother plants. Usually, meristems of virus-infected plants are virus-free, and by culturing meristems, virus-free plants can often be obtained. A detailed description of such methods was given in Section 7.2.

In contrast to meristem cultures, callus cultures or cell suspensions often produce more plants able to be transplanted to soil. For many plant species, however, it is difficult to find suitable culture conditions to satisfactorily induce propagation by these methods. Cytogenetic stability and homogeneity are higher in plants derived from meristem cultures than in those of callus or cell suspension origin. The greatest number of plants per setup can be produced by somatic embryogenesis, associated with a high level of cytogenetic homogeneity. Here, some possibility for automatic processing in bioreactors (fermenters) exists, which would reduce the manual labor required for either meristem or callus cultures, with inductions of caulo- and rhizogenesis to produce plants (Sects. 2.2 and 7.3).

Another important area of application of cell and tissue cultures is plant breeding. In this case, high numbers of genetically identical plants are commonly required for crossbreeding to obtain hybrids for practical plant production. To obtain such plant material, either meristem cultures, or plants produced by somatic embryogenesis can be employed. A requirement for somatic embryogenesis exists also in the use of protoplast fusion products in plant breeding. By fusion of protoplasts of different genomes, a new genome is produced that can be used in conventional plant breeding programs. For this, the regeneration of the fusion products to be raised into intact and flowering offspring is necessary. The same requirement exists for dihaploid plants out of anther cultures to be used for breeding. All these examples are potential possibilities to improve practical plant breeding; after some initial success, however, these have not yet been really applied on a large scale.

Today, somatic embryogenesis is a prerequisite to produce transgenic plants. About 15 years ago, the first genetically modified (GM) crops were introduced to practical agriculture; the original acreage of about 3 million hectares soon increased, and by 2008, the global hectarage of biotech crops continued to grow strongly reaching 125 million hectares, up from 114.3 million hectares in 2007. this translates to an “apparent growth” of 10.7 million hectares (the sixth largest increase in 13 years) or 9.4% measured in hectares, whereas the “actual growth”, measured more precisely in “trait hectares”, was 22 million hectares or 15% year-on-year growth, approximately double the “apparent growth” more precisely, 166 million “trait hectares” (Jame 2009). Main GM crops were cotton, maize, rapeseed, and soybeans. In terms of economic considerations, differences in the yields of conventional and GM crops were generally negligible. In Spain, growing Bt maize for three seasons increased the yield by only about 5%. Main advantages are usually considered to be easier weed control, and savings on pesticides, tillage, labor, and machinery costs. As reported from China, farmers use five times less insecticides for Bt cotton, and in India a net saving of € 25 per hectare was recorded. In the USA, however, farmers reported that the financial gain from reduced pesticide application to GM crops was more or less outweighed by higher costs of seeds. Still, optimism prevails—e.g., growing herbicide-resistant sugar beet in the UK has been estimated at € 33.5 million/year. The successful use of GM crops seems to depend mainly on selecting the right crop, and the right trait for a given location, possibly after some conventional breeding.

After some initial success, usually on a laboratory scale, application is still very limited also in a third field of practical application, namely, the use of cell and tissue culture to produce secondary metabolites on a commercial scale (see Chap. 10). Though many compounds of commercial interest, mainly products of secondary metabolism, have been detected in cell and tissue culture systems, their concentrations are mostly too low to be exploited commercially. More success was obtained by using cell cultures to transform cheap raw products into commercially highly valuable compounds. Some early examples of such systems are the transformation of digitoxin into digoxin using cell cultures of Digitalis, or the synthesis of atropine and scopolamine from tropine and tropic acid as substrates in cell cultures of Datura. Also here, however, the high selling price of the drug in pharmacies limits large-scale commercial application. For compounds of commercial interest to be produced by culture systems, it needs to be considered that very well-developed conventional methods are available to the industry, using raw material produced by agriculture. Thus, to convince industrial companies to rather use cell culture systems, it is not enough to produce a substance at equal costs, as is the case for the Digitalis system. Such a change in the production technique requires, among other, high investments in equipment, and thorough training of personnel. To shift from the conventional production system to a cell culture system, the production costs of the latter should be much lower than that of the former (maybe half). Challenges lie ahead. Notably, all hope of discovering unknown substances for use as drugs in medicine has to date been in vain. Ever-present competitors to the application of cell culture systems are chemical synthesis, and the use of immobilized enzymes in the industrial production of organic compounds. Nevertheless, the era of gene technology has only just begun, and new fields of research like metabolomics will contribute to a better understanding of the working “machinery” of cells, with new perspectives as a basis for the commercial use of such systems.