V.W.H. Campbell, Post-Gazette Valerie Oke in her lab at the University of Pittsburgh -- "I had a terrible biology class in high school. But my mother urged me to give it a second try."

By Mark Roth
Pittsburgh Post-Gazette The typical soybean field in Western Pennsylvania contains 1¹/₂ million plants.

And that gives Valerie Oke several hundred million nodules to love.

Nodules are the tiny bumps on the roots of legumes like soybeans, alfalfa and clover that convert nitrogen into a usable form so the plants can grow and prosper.

Valerie Oke Age: 39 Position: Assistant professor, Department of Biological Sciences, University of Pittsburgh. Education: Bachelor of arts, Bryn Mawr College, 1984; Ph.D. in cellular and developmental biology, Harvard University, 1994; Postdoctoral fellow, Stanford University, 1994-97. Previous positions: Research associate, Stanford University, 1997-99. Professional honors: National Science Foundation postdoctoral fellowship in plant biology, 1994-97. Publications: Nine referred papers in scientific journals, plus a 1999 review with Dr. Sharon Long of rhizobium-legume symbiosis. The Series Click here to view other installments in this continuing series.

Each nodule hosts an intricate dance between the plants and a soil bacteria known as rhizobium, and it is that process that Dr. Oke has spent several years studying.

Dr. Oke, a biology professor at the University of Pittsburgh, is working to unravel the genetic secrets that allow the plants and bacteria to coexist.

That knowledge might someday make it possible to tweak the biological system to pump out more crop-enriching nitrogen, she said, which eventually might reduce the world's heavy and sometimes harmful use of nitrogen fertilizers.

Plants, animals and human beings all need nitrogen to create the building blocks of life -- DNA and proteins. And this would seem an easy task. After all, we're bathed in nitrogen, which makes up 78 percent of Earth's atmosphere.

But plants can't use atmospheric nitrogen until it's converted into ammonia and other nitrogen compounds, and that process requires a lot of energy because gaseous nitrogen is a "tightly bound" molecule, Dr. Oke said.

"It's two nitrogen atoms connected by a triple bond. So that triple bond is very strong."

One way to break the bond is with lightning, which produces some of the nitrogen that enriches soil naturally.

But the main source of this "nitrogen fixation" are soil bacteria, including the rhizobium bacteria, that set up little nitrogen conversion factories inside legumes.

Over the eons, the plants and the bacteria have developed a finely tuned partnership.

It starts when the legumes sense that there is too little nitrogen in the soil. At that point, they exude substances called flavonoids, which signal the rhizobium to migrate to the plants.

The bacteria enter the plants through their delicate root hairs. Once inside, they strike a bargain. The bacteria will produce ammonia to fortify the plant, and the plant will provide sugar to feed the bacteria.

Until nitrogen fertilizers came along about a century ago, this was how most of the world's soil got its critical supply of nitrogen. And that posed a problem.

Two of the world's most important food crops -- corn and rice -- cannot create their own nitrogen, which limited how much corn and rice could be grown, which limited how many people the Earth could support.

The Haber-Bosch process, developed by two German chemists in the early 1900s, changed all of that by creating an efficient way to synthetically manufacture ammonia.

The process was invented to create nitrogen compounds for explosives in World War I, and even though Fritz Haber won the Nobel Prize for his discovery in 1918, he never received much acclaim because he went on to develop poison gases for the Germans in World War I and the precursor of the gas used in Nazi concentration camps in World War II.

Eventually, the Haber-Bosch process was adapted to make nitrogen fertilizer, which helps to grow the food that sustains an estimated 40 percent of the world's population.

But using so much nitrogen fertilizer comes with a cost, Dr. Oke said.

First, she said, "you make all this nitrogen fertilizer and you put it on your plants, but not all the fertilizer you put on is being incorporated in the plants. A lot of it is coming off the fields."

That runoff contributes to algae growth that creates oxygen-depleted "dead zones" along America's coastlines.

The process used to manufacture the fertilizer also consumes a lot of fossil fuel. Dr. Oke said one study in the mid-1990s indicated that 5 percent of the world's natural gas supply was used to produce nitrogen fertilizer.

Finding ways to produce more natural ammonia in the soil therefore might be very helpful to the environment, she said, and the research she and other scientists are doing holds out the hope of "taking the legumes we already have and boosting the whole system up."

One indication of how helpful is the impact that crop rotation already has in reducing the need for nitrogen fertilizer. Greg Roth, a Penn State University agronomy professor, said that growing soybeans in a field the year before growing corn can cut the fertilizer needed for the corn by 40 percent.

Dr. Oke's contribution to this effort has been to focus on understanding the genes that allow the legumes and bacteria to coexist. She has found two genes in rhizobium that seem to play a critical role in the formation of the nodules and the nitrogen conversion process, but her lab is still trying to figure out exactly how they work.

Dr. Oke grew up in Pasadena, Calif. She may have been inspired to become a professor by her father, who was an astronomer at the California Institute of Technology for nearly 30 years.

But it's her mother who's responsible for her interest in biology.

"I had a terrible biology class in high school," Dr. Oke recalled. "But my mother urged me to give it a second try."

More than 20 years later, she's still at it.