Chap. 10. The Geosphere, Soil, and Food Production 273been genetically engineered to produce their own insecticide. Plants produced by this
method are called transgenic plants. During the 1970s, the ability to manipulate DNA
through genetic engineering became a reality, and during the 1980s, it became the basis
of a major industry. This technology promises some exciting developments in agriculture
and, indeed, is expected to lead to a “second green revolution.” Direct manipulation of
DNA can greatly accelerate the process of plant breeding to give plants that are much
more productive, resistant to disease, and tolerant to adverse conditions. In the future,
entirely new kinds of plants may even be engineered.
Plants are particularly amenable to recombinant DNA manipulation. In part this is
because huge numbers of plant cells can be grown in appropriate media and mutants can
be selected from billions of cells that have desired properties, such as virus resistance.
Individual plant cells are capable of generating whole plants, so cells with desired
qualities can be selected and allowed to grow into plants which may have the qualities
desired. Ideally, this accomplishes in weeks what conventional plant breeding techniques
would require years to do.
There are many potential green chemistry aspects from genetic engineering of
agricultural crops. One promising possibility is to increase the efficiency of photosynthesis,
which is only a few tenths of a percent in most plants. Doubling this efficiency should
be possible with recombinant DNA techniques, which might significantly increase the
production of food and biomass by plants. For example, with some of the more productive
plant species, such as fast-growing hybrid poplar trees and sugarcane, biomass is almost
economical as a fuel source. A genetically engineered increase in photosynthesis efficiency
could enable biomass to economically replace expensive petroleum and natural gas for
fuel and raw material. A second possibility with genetic engineering is the development
of the ability to support nitrogen-fixing bacteria on plant roots in plants that cannot do
so now. If corn, rice, wheat, and cotton could be developed with this capability it could
save enormous amounts of energy and natural gas (a source of elemental hydrogen) now
consumed to make ammonia synthetically.
Transgenic crops have many detractors, and demonstrations have broken out and
test plots of crops destroyed by people opposed to what they call “Frankenfoods.” There
is some evidence to suggest that bacterial insecticide produced by transgenic corn kills
beautiful Monarch butterflies that have contacted the corn pollen. In year 2000 a lot of
concern was generated over the occurrence of transgenic corn in taco shells made for
human consumption, and a large recall of the product from supermarket shelves occurred.
Opposition has been especially strong in Europe, and the European Commission, the
executive body of the European Union, has disallowed a number of transgenic crops.
Despite these concerns, transgenic crops are growing in importance and there is a lot of
interest in them in highly populated countries, particularly China, where they are seen as
a means of feeding very large populations.
The Major Transgenic Crops and their Characteristics
The two characteristics most commonly developed in transgenic crops is tolerance
for herbicides that kill competing weeds and resistance to pests, especially insects, but