A simple genetic change enables plants to more efficiently take up and use nitrogen, the principal nutrient in fertilizer, researchers now report. Such changes in crop plants could help maintain yields while reducing farmers' dependence on polluting fertilizers.
Farmers in much of the world apply nitrogen-based fertilizer to their land, allowing them to reap richer harvests. All that fertilizer adds roughly 100 million tons of nitrogen to the biosphere--about as much as is produced naturally by all life on Earth. Nitrogen runoff from fields pollutes drinking water in rural areas and creates large dead zones in the world's coastal seas (ScienceNOW, 8 November 2001). To cut the need for fertilizer, researchers have sought to develop crop plants that use nitrogen more efficiently. Genetic engineers had tried to boost enzymes that help plants take up the two most common forms of nitrogen, nitrate and ammonia, and convert them into amino acids and proteins needed for growth. But it didn't make plants any more efficient. Shuichi Yanagisawa of Okayama University in Kurashiki, Japan, and his colleagues took a different tack. Plants assimilate nitrate and ammonia by hanging them on branches of small sugarlike compounds, like ornaments on a Christmas tree. The Japanese researchers added a corn gene called Dof1 that activates several genes that help produce those sugary compounds, thereby giving plants more places to attach nitrogen. The strategy worked. Arabidopsis plants with an incorporated Dof1 gene had higher than ordinary levels of the sugarlike compounds. They had nearly twice the normal level of amino acids, and they incorporated 28% more nitrogen into their tissue. And under low-nitrogen conditions, which caused normal plants to wither and turn yellow, the engineered plants remained green and healthy. The researchers also obtained similar but preliminary results in potato plants, they report online this week in the Proceedings of the National Academy of Sciences. "It's an important breakthrough," says plant molecular biologist Nigel Crawford of the University of California, San Diego. But although excited by the findings, he cautions that researchers will need to check whether the genetic tweaks caused any side effects--such as making the plants tastier to insects--that would make them less useful for crop plants. "You need the big picture," Crawford says.