Crop Plants And Renewable Resources

With the Arabidopsis genome in hand, plant scientists are now eagerly looking for sequence data for crop plants such as rice and maize (48). In these cases the scientific challenge of genome sequencing is much bigger because these plants have genomes 4 to 25 times larger than the Arabidopsis genome. This results from the tendency of many plants to carry duplicate or multiple copies of large sections of DNA. In view of the economic importance of rice and maize as staple food for more than half of the world's population, the results of such projects will undoubtedly form the basis for better knowledge of the genetics of these plants. These efforts will eventually also lead to continued progress in improving the productivity and the quality of these crop plants. Thus, a challenging and fascinating chapter of plant biotechnology will be opened in a few years (48).

In general, the productivity of modern agricultural crop plants has been increased manyfold over the last decades. Adaptation of the various genotypes either to the often complex factors of the environment (i.e., soil, climate, temperature, water supply), to the specific prevailing agricultural conditions, or to pests and pathogens has been achieved very successfully at sometimes impressive speed. Furthermore, the different demands of markets and consumers with regard to product quality and fields of product application have been leading guides in the breeding programs. These programs were conducted by conventional techniques of crossing and selection, but more recently molecular biological procedures [e.g., restriction fragment length polymorphism (RFLP)] have also been introduced. In general, in addition to yield and quality, modern agricultural crop plants have been optimized for high consumption of fertilizers and water. This last aspect will have to be at least partly reversed because future agricultural practice in many countries will be confronted by a reduced water supply. Plants with appropriate mechanisms for low water management are a challenging scientific task in the future.

A few lines of foreseeable development in plant breeding and construction are certain. Plant breeding will more and more apply molecular biological and gene technological methods. The data from genome sequencing programs will be essential prerequisites. The diversification of lines within a given species will increase because of the diverse demands for product quality and product application. The overall productivity of our crop plants has to be greatly increased in order to feed the rapidly growing population.

A very interesting and scientifically important step into this modern field has been taken by the recent release of "Golden Rice." This transgenic rice supplies provitamin A and iron and is expected to reduce major micro-nutrient deficiencies in substantial populations where rice is the major diet (49). Iron deficiency (a health problem in many women) is compensated by several transgenes leading to better iron uptake and hydrolysis of phytate. Vitamin A (required to prevent eye problems and blindness) is provided by substantial levels of /3-carotene accumulating in the rice grains due to four transgenes to allow carotinoid formation.

The wide field of renewable resources represents a further challenge for plant biotechnology and modern agriculture. Petrol oil and many mineral oil-derived chemicals as well as coal are to be replaced by plant biomass or plant-derived raw materials, various chemicals, biopolymers, and all sorts of high-molecular or low-molecular products formed by and isolated from plants. Such plant production requires little if any exhaustable energy resources.

Potato lines with structurally modified starch (changes in amylose/ amylopectin ratios), rape transgenic genotypes accumulating seed oil with other than the normal C16 and C18 fatty acids, or crop plants mainly storing fructans instead of sucrose in their roots are well-established suitable examples (50). From rape-derived "bio-diesel" as petrol for cars to highly sophisticated organic chemicals from suitably constructed plant lines, the design of new "industrial plants" opens wide possibilities for plant biotechnology on a practically unlimited scale.

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