A discovery by a team of University of Missouri (MU) researchers could be the first steps toward helping crops use less nitrogen fertilizer.  Nitrogen fertilizer costs U.S. farmers approximately $8 billion each year, and some of the unused or excess fertilizer can find its way into rivers and streams, damaging the delicate water systems.  Getting to self-fertilizing crops, especially those for food and fuel would benefit both consumers and the ecosystem as well.

Gary Stacey, an investigator in the MU Bond Life Sciences Center and professor of plant sciences in the College of Agriculture, Food and Natural Resources, found that crops, such as corn, are “confused” when confronted with an invasive, but beneficial, bacteria known as rhizobia bacteria.

Soybean Rhizobia Bacteria Filled Root Nodules. Click image for the largest view.

Soybean Rhizobia Bacteria Filled Root Nodules. Click image for the largest view.

When the rhizobia bacteria interact correctly with a crop, the bacteria receive some food from the plant and, simultaneously, produce nitrogen that most plants need. In his study, Stacey found that many other crops recognize the bacteria, but do not attempt to interact closely with them.

Stacey explains, “The problem is that corn, tomatoes and other crops have a different response and don’t support an intimate interaction with the rhizobia, thus making farmers apply larger amounts of nitrogen than might otherwise be necessary,” Stacey said. “Scientists have known about this beneficial relationship since 1888, but it only exists in legume crops, like soybeans and alfalfa. We’re working to transfer this trait to other plants like corn, wheat or rice, which we believe is possible since these other plants recognize the bacteria. It’s a good first step.”

When legumes like soybeans sense a signal from the bacteria, they create nodules on the roots where the bacteria gather and produce atmospheric nitrogen that the plants can then use to stimulate their growth.  But, this reaction doesn’t happen in other plants.

The team’s research paper was published this month in the journal Science.

Yan Liang, a co-author of the study and post-doctoral fellow at MU explains further, “There’s this back and forth battle between a plant and a pathogen. Rhizobia eventually developed a chemical to inhibit the defense response in legumes and make those plants recognize it as a friend. Meanwhile, corn, tomatoes and other crops are still trying to defend themselves against this bacteria.”

In the study, Stacey and Liang treated corn, soybeans, tomatoes and other plants to see how they responded when exposed to the chemical signal from the rhizobia bacteria. They found that the plants did receive the signal and, like legumes, inhibited the normal plant immune system. However, soybeans, corn and these other plants don’t complete the extra step of forming nodules to allow the bacteria to thrive.

“The important finding was that these other plants didn’t just ignore the rhizobia bacteria,” Stacey said. “They recognized it, but just activated a different mechanism. Our next step is to determine how we can make the plants understand that this is a beneficial relationship and get them to activate a different mechanism that will produce the nodules that attract the bacteria instead of trying to fight them.”

Food and biofuel crops are all going to need an increasing amount of fertilizer to meet the consumer’s demands.  Without nitrogen fertilizer much of the world’s people wouldn’t get a diet adequate for survival.  And the future holds an ever-growing biofuel demand that also will need nitrogen fertilizers.

Today most nitrogen fertilizer is made using natural gas for the source of the hydrogen to make the NH3 compound that is the precursor to the plant’s nitrogen needs.  While there isn’t a suggestion that the rhizobia bacteria would eliminate nitrogen fertilizer, more crops using the rhizobia contribution would save a great deal of money and offer more lower cost food and fuel supplies.


2 Comments so far

  1. Mark Shults on October 2, 2013 7:16 PM
  2. JP Straley on October 3, 2013 7:54 AM

    What are weeds but plants in the wrong place. Plants with this mod could turn out to be at great advantage, just as leguminous plants Can Dom some ecosystems. If this metabolic trick were added to commercial tree species and escape to the wild, it could result in very different forest structure and a reduction in plant diversity…very undesirable.

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