Wild tobacco heeds ‘ouch’ from sagebrush

Field biologists say they’ve found a case of the much-debated possibility that plans of different species communicate in the wild.

When researchers clip sagebrush, nearby tobacco plants seem to boost their defenses and reduce damage from grasshoppers and cutworms, report Richard Karban of the University of California, Davis and his colleagues.  They detected a volatile chemical wafting from wounded safebrush and, perhaps in response, extra defensive chemical in the tobacco, the researchers say in the current OECOLOGICA (vol. 125, issue 1).

Such a paper “is a wonderful addition to a rapidly growing research field,” comments Marcle Dicke of Wageningen University in the Netherlands, who’s organizing a special journal issue on the topic.

The thought of plant communication has riled biologists for nearly 20 years, Karban says.  Early outdoors experiments sparked criticisms about methods, such as charges that the study plots weren’t laid out to allow truly independent trials.  Some experimental designs yielded conctradictory results, Karban says.

Laboratory tests in sealed chambers showed that substances released by injured plants trigger chemical changes in neighbors, Karban says.  Yet this evidence left big-picture biologists wondering about the real world. “A lot of ecologists are pretty cynical about it,” Karban says.

He and his colleagues tested the notion of plant communications in California’s Sierra Nevada mountains.  Clipping sagebrush brushes led to a 10-fold rise in the concentration of methyl jasmonate, a volatile compound that in the lab prompts tobacco to churn out compounds that sabotage insect metabolism.

One of smoking tabocco’s wild cousins, Nicotiana attenuata, grows in the area, but researchers transplanted it to standardize its distance from sagebrush plants.  Tobacco plants near clipped safebrush showed roughly four times the activity of the enzyme polyphenol oxidase (PPO) compared with plants nestling by unmolested sagebrush. Lab tests had linked PPO to chemical defense.

Tobacco plants near clipped sagebrush suffered less than half the insect damage seen in tobacco near intact bushes.  The researchers repeated the experiment in two subsequent years and saw a smaller but still significant difference.  They also found that barriers in the air, but not those in the soil, block the effect.

Judith Myers of the University of British Columbia in Vancouver calls the work “carefully done,” noting the three repetitions of the experiment.  She wants to know whether preventing the observed amount of insect damage matters evolutionarily, she says.  Other than that, it’s a question of how you define communication, she says. “If I smell smoke and run from a burning house, was that communication between the fire and me?”

The scenario of plants sounding alamrs often gets dubbed “talking trees,” Karban says. “I hate that phrase.”  While he describes his plants as communicating, he adds qualifications.  An injured plant may give off the supposed alarm compounds involuntarily, he suggests.  “Why should they talk?”  Karban asks.  “At least say, ‘listening trees.’ “