His finalist year: 1972

His finalist project: A study of the plant diversity on the hills outside of Los Angeles

What led to the project: From an early age, plants fascinated Jonathan Gershenzon, who grew up in Los Angeles in the 1950s and '60s. In particular, the young naturalist was drawn to their scents. In high school, encouraged by one of his science teachers, he checked books out of the library on plant ecology and then hiked up into the hills outside Los Angeles to study the chaparral (dense drought-resistant shrubs and dwarf trees that cover the region, and play a key role in area wildfires). He stretched a rope grid over a section, and documented the prevalence of the different shrubby species—wild lilac, manzanita, sagebrush. Then he'd take a picture and move the rope grid to another elevation or hill.

He was amazed by the different compositions of different chaparral communities even in relatively close plots. He was able to show that distance from the ocean played a big role in this diversity, and he later learned that the composition of the chaparral was, in large part, a function of how recently the area had burned. He never tested that thesis, he says. But "somebody saw a little promise there" in a kid willing to spend his vacation with his nose buried in California's native vegetation. When he entered his project in the 1972 Westinghouse Science Talent Search, he was named a finalist.

The effect on his career: Gershenzon became a biology major at the University of California, Santa Cruz, and began to study the chemistry of "all these wonderful smells" plants produced. That's how he learned about a group of chemicals known as terpenes. These chemicals can make plants smell good or, alternately, noxious. (They are also the active—and some say potentially toxic—ingredients in many household cleansers.)

"For years, people thought they were a waste somehow," he says—that is, not necessary to plant growth or reproduction. But Gershenzon came to understand that terpenes are most likely defenses against pathogens or insects, or signals to "other members of the natural community."

He went to the University of Texas at Austin to earn a PhD in plant chemistry, doing his dissertation on terpenes found in the wild sunflowers native to the southern and eastern U.S. He and an undergraduate assistant spent their summers driving around the Southeast collecting sacks of wild sunflower samples whose more volatile terpenes proceeded to stink up their backseat, their campsites, and their hotel rooms. "We had some of the same adventures of more typical road-trips," he says, with people getting suspicious of two young men hanging out in fields and stuffing weeds into their car. "We had people call the police on us." Nevertheless, he earned his PhD in 1984.

After that, he spent several years doing research at Washington State University in Pullman, studying the enzymes involved in producing terpenes. He learned that sometimes the same pathways could produce different compounds, introducing an element of statistical chance into the scent of a plant. This could help generate the diversity of aromas present in wild populations.

In 1997 he had accepted a faculty position at Michigan State University in East Lansing, but instead took an offer from the Max Planck Society to go to Germany to start a new institute devoted to chemical ecology. The idea of building something appealed to him. So he packed his bags and started learning German.

What he's doing now: These days, Gershenzon is the managing director of the Max Planck Institute for Chemical Ecology in Jena, Germany. (His language skills are still a work in progress, he notes, but his German-born children are happy to correct him.)

His research looks at using modern molecular methods to manipulate plant characteristics and to isolate and test the effects of terpenes. Although fascinating for a scent enthusiast in its own right, this work has practical implications for agriculture. For instance, Gershenzon and colleagues published a study in Nature in 2005, which found that when the corn root worm attacks corn, the plant produces a terpene that attracts the nematode, a roundworm. Nematodes, conveniently enough, eat root worms. Unfortunately, for most North American corn varieties this defense has been bred out during development—probably accidentally, but at an unforeseen cost.

"Chemical defenses are one of the major factors that determine plant success. Without them, the world wouldn't be as green as it is," says Jack Schultz, director of the Christopher S. Bond Life Sciences Center at the University of Missouri–Columbia. "How defense production is controlled at the gene level is critical for breeding or engineering crop and other plants that are more resistant to pests." Gershenzon's work, he says, has greatly expanded knowledge of how plants make and use terpenes.

After years of sticking his nose in plants, Gershenzon has developed quite an appreciation for the sense of smell, particularly its link to memory and our survival as a species. "It's how our simian ancestors kept themselves from being poisoned," he says. Now, "some of the local women in the market smell every piece of fruit," but this is a dying appreciation. Few people have such finely tuned noses and favorite scents. As for Gershenzon, "I'm still biased to the mint family—peppermint and spearmint, thyme, sage and oregano." Although, "I like flowers, too," he adds. "It'd be hard to choose just one."