Most of the development of commercial GM crops
has been focused on pest and herbicide resistant crops (Pretty, 2001). Pest resistant Bt crops were one of the
first to be commercialized and have, thus far, proven effective (Conway, 2000). In
1999, a short 4 years after the first commercial GM pest/herbicide
resistant crops, approximately 40% of U.S. corn, soybean, and cotton fields were planted with
such GM crops (Kalaitzandonakes, 1999).
Pest/herbicide resistance can be conferred in
a number of ways:
gene transfer where Agrobacterium vectors
carrying a promoter sequence, a terminator sequence, and the desired gene
are transformed into the plant cell nucleus. This process is good for dicot species (e.g.
tomato, potato, rapeseed), but not normally good for monocot species,
although it does work with rice (Jung, 2000).
bombardment” with DNA coated tungsten or gold particles may be used to
transform all plant species. The DNA
is released into the cell during its travel, and can be incorporated into
the cell nucleus. This event is
rare, and this technique must be performed on plant tissue that can regenerate. This process has been used to transform
millet, barley, wheat, rice, papaya and maize (Jung, 2000).
CaCl2 and PEG can be used to transform plant protoplasts, and
then grown into whole plants. This
method has been used to transform maize and rice (Jung, 2000).
plastid DNA is a recent development.
Desired traits are integrated using homologous recombination between
the DNA construct and the plastid DNA.
This method has not been successful with crops as of yet, but would
be advantageous since it would result in high expression rates. Also, the resistance would not be passed
to future generations through pollen, an important environmental concern
To learn how pest/herbicide resistance works
on the genetic level:
or comments can be directed to email@example.com
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