In genetically engineered plant cells, a bacterium Agrobacterium is mainly involved in transfer of foreign gene. However, Agrobacterium cannot infect all plants since it has a narrow range of host specificity. Therefore other techniques have been developed to introduce foreign DNA into plant cells. Novel methods of ensuring DNA uptake into cells include electroporation and mechanical delivery or biolistics.
Electroporation is a process of creating temporary pores in the cell membrane by application of electric field. Creation of such pores in a membrane allows introduction of foreign molecules such as DNA, RNA, antibodies, drugs, etc. into cytoplasm. The development of this technique is due to contribution of biophysics, bioengineering, cell and molecular biology. While the technique is now used widely to create transgenic microorganisms, plants and animals, it is used increasingly for application of gene therapy.
The mechanical particle delivery or gene gun methods to deliver DNA on microscopic particles into target tissue or cells. The process is increasingly used to introduce new genes into a range of bacterial, fungal plant and mammalian species. It is the main method of choice for genetic engineering of many plant species including rice, corn, wheat, cotton and soyabean.
Presently, more than 50 types of genetically engineered plant species, called transgenic plants have been successfully developed. These plants were made to resist insect pests, viruses or herbicides through incorporation of foreign gene into DNA of host plant cells. Initially transgenic plants were developed more in dicotyledons, but now extended to several monocotyledons like wheat, maize, rice and oats. Transgenic plants have also been developed and are suitable for food industries (delaying ripening in tomato).
Gene pharming, the use of transgenic plants as bioreactors or factories for production of speciality chemicals and pharmaceuticals is being pursued by a number of firms. Plants have been engineered to produce human proteins, such as hormones, in their seeds. A weed called mouse-eared cress has been engineered to produce a biodegradable plastic (polyhydroxybutyrate, or PHB) in tissue granules.
1. Nicotiana tabacum
2. Beta vulgaris
3. Glycine max
4. Helianthus annuus
5. Solanum tuberosum
6. Gossypium hirsutum
1. Asparagus sp. 3. Zea mays
2. Oryza sativa 4. Avena sativa
Under normal circumstances, herbicides affect photosynthesis or biosynthesis of essential amino acids. Under field conditions, application of herbicides not only kills the unwanted weeds but also greatly affects the field crops. In order to protect the crops against exposure to herbicides, scientists after intensive research isolated a gene from Streptomyces hygroscopicus which encodes an enzyme, capable of inactivating the herbicide 'Basta'. Transgenic plants with this gene have been developed, demonstrating effectiveness of this gene for protection against herbicide 'Basta'. Thus, herbicide-tolerant crop plants have now been developed by genetically manipulating plant genomes resistant to specific herbicides.
Genes from Bacillus thuringiensis (Bt2) have been introduced into several crops, including tomato and cotton, and field-testing has demonstrated impressive results against many pests. Spore preparation of this bacterium is used as a biological insecticide during the last 20 years. Insecticidal activity depends on a toxic protein called delta endotoxins. The toxin gene (Bt2) from Bacillus thuringiensis has been isolated and used for Agrobacterium. Ti plasmid mediated transformation of tobacco, cotton and tomato plants. The transgenic plants were resistant to the Manducta sexta, a pest of tobacco. India had acquired technology from U.S.A. for introducing Bt toxin gene in cotton for the development of resistance against pests in this major cash crop of India. Widespread use of insecticides, fungicides and pesticides for crop protection undoubtedly has damaging effects on the environment and hence it is important to improve the control of pests and diseases by genetic means. Genetic modification of plants is an attempt for ecofriendly measures against environmental degradation.
Through genetic modification, the oil-producing soya bean was tailored to produce a wide range of industrial lubricants, cosmetic compounds and detergents that are biodegradable. A whole new area of biotechnology has been opened up and plants are made to synthesize many novel substances including functional human antibody fragments.