Greenery on alert

Combating bioterrorism is no longer the domain of high-tech gadgets alone.

A new breed of genetically engineered plants will soon be capable of functioning as "sentinels," detecting harmful chemical and biological agents in the atmosphere. Designed to turn fluorescent green or a sickly brown within minutes or hours of exposure, the plants could be used along airport runways or around military or industrial sites.

"Plants make good sentinels because they can't run away," says Jack Schultz, a chemical ecologist and professor of entomology at Pennsylvania State University. "Because they are rooted in their environment, they must respond dynamically to environmental changes."

Some of the plants being developed will be able to signal the presence of chemical agents and animal pathogens such as anthrax. Others are being designed to fluoresce upon detecting TNT residues in the soil, aiding in land mine detection. If enough plants are gathered in one place, and if their glow is bright enough, researchers say satellites may be able to detect minefields from space.

Schultz, with Ramesh Raina, heads the Penn State research team conducting the $3.5 million project, which is sponsored by the Defense Advanced Research Projects Agency (DARPA).

By 2006, the scientists hope to have created around 300 lines of sentinel plants to test out in nature. Currently, their work centers on Arabidopsis, or mouse-ear cress, a small flowering plant from the mustard family. Dr. Raina says the plant is the most studied on earth, and the only one whose entire genetic sequence has been mapped and is publicly available.

Engineered to produce one of two consistent responses, the plants will change color, simulating diseased plants, upon exposure to a wide variety of chemical and biological agents. Effects are expected to be temporary, lasting anywhere from a few hours to a few days.

Meanwhile, in another DARPA-funded venture building on the work of the Penn State scientists, Colorado State University biologists June Medford and A.S.N. Reddy are constructing a de-greening circuit that aims to make plants rapidly lose their green color in response to harmful agents. The researchers say such detector systems could also be introduced into algae in aquatic areas, allowing satellites to monitor any color change in response to adverse elements in the environment.

"The plants would provide warnings so people could immediately vacate an affected area, and then experts could verify exactly what the agent is," says Dr. Reddy. "Unlike the [federal government's current] Bio-Watch plan [to use EPA air-quality monitoring stations to detect deadly germs such as anthrax or smallpox,] which would take 12 to 24 hours to detect and report pathogens, the plants would give nearly immediate warnings."

"Plants are sensitive enough to detect a difference in even one gene in a fungal spore," adds Dr. Medford.

In a statement issued by DARPA, the agency said: "If successful, these efforts will create fundamentally new detection capabilities via organism engineering, such as the ability to detect explosives or chemical warfare agents via remote observation."

The scientists hope to test the first set of "performing plants" in a laboratory setting three years from now. The researchers hope to develop "plug-and-play kits," which could ultimately be inserted into a variety of ornamental and horticultural plants.

While remaining somewhat skeptical of the sensitivity and the limits of such a detection scheme, experts nevertheless are optimistic about its potential.

"The idea of a natural biosensor is clever, and there is a wealth of biotechnology to draw on," says Robert Levis, director of Temple University's Advanced Photonics Research program. "This technology would probably be of more value in cities that are worried about external threats than in a battlefield application where there may be limited vegetation [such as Iraq]."

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