Figure 4.5

Most plants can't survive in nitrogen-poor soils without the addition of nitrogen fertilizers Not so for legumes like this soybean plant, whose  bacteria-filled nodules keep it supplied with a rich source of nitrogen. Can  biotechnology be used to help legumes produce even greater amounts of  nitrogen in usable forms? Can other plants like corn, wheat, or rice be  engineered to have this same "nitrogen-fixing" ability?

nodules on the roots of leguminous plants such as clover and soybeans. These "nitrogen-fixing" bacteria convert nitrogen from the air into ammonia, a form of nitrogen the legumes can use. Rhizobium also releases ammonia into the soil where other bacteria convert it to nitrates, acting as natural fertilizers for other plants.

Researchers have identified genes that enhance the nitrogen-fixing process, as well as genes involved in the mechanism by which bacteria attach to leguminous host plants. They hope to modify the genes to boost bacterial efficiency, and to substitute these more efficient strains on the roots of particular crops. It has been estimated that a one percent improvement in the efficiency of nitrogen use could mean a saving of $320 million per year in the amount spent on fertilizers in the United States.