Recombinant DNA and biotechnology have been used to increase plant growth by increasing the efficiency of the plant's ability to fix nitrogen. Scientists take genes for nitrogen fixation from bacteria and place the genes into plant cells. Because of this, plants can obtain nitrogen directly from the atmosphere. The plants can produce their own proteins without the need for bacteria. Another way to insert genes into plants is with a recombinant tumor-inducing plasmid Ti plas-mid. This is obtained from the bacterium Agrobacterium tumefaciens. This bacteria invades plant cells and its plasmids insert chromosomes that carry the genes for tumor induction. An example of recombinant DNA with livestock is the recombinant bovine growth hormone that has been used to increase milk production in cows by 10 percent.
U.S. farmers grow substantial amounts of genetically modified crops. About one-third of the corn and one-half of the soybean and cotton crops are genetically modified. Cotton and corn have become resistant to herbicides and insects. Soybeans have herbicide resistance and lower saturated fat content. Having herbicidal-resistant plants is important because many crop plants suffer stress when treated with herbicides. Resistant crops are not stressed by the chemicals that are used to control weeds.
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