Plants: New Anti-Terror Weapon? By Lakshmi Sandhana
Story location:,58118,00.html

02:00 AM Apr. 05, 2003 PT

Green and leafy, working 24 hours a day in a diverse range of environments, the newest recruits in the fight against terrorism could soon be trailing alongside your windowsill or eyeing you from the corner of the room.

As concerns grow over the threat of bioterrorism, researchers are developing an early-warning system using plants that can detect and signal the presence of harmful chemical or biological agents.

Thanks to a three-year, $3.5 million grant from the Defense Advanced Research Projects Agency, Penn State scientists are laying the groundwork for these so-called "sentinel plants," which are genetically engineered to perform their anti-terrorism tasks.

"Plants are exquisitely attuned to their environments and are extremely dynamic," said Jack Schultz, a chemical ecologist and professor of entomology at the College of Agricultural Sciences. "I like to say they're just very slow animals because they have to deal with the world as it comes to them, since they can't move away."

Because plants are rooted in their environment, they must respond dynamically to environmental changes, Schultz said. Many of these responses can be observed or measured, such as changes in color, shape or growth rate.

For example, a houseplant that does not get fertilized may not grow well and may change color. In doing so, the plant is reporting the conditions it's experiencing in its soil.

"In essence, it's telling you, 'feed me,'" Schultz said. "The trick is to design plants that respond in particular ways to particular stimuli and to amplify these responses so they can be detected readily."

Ramesh Raina, an assistant professor of biology at Penn State's Eberly College of Science, believes the key to manipulating plant responses to environmental stimuli lies in understanding the role of certain genes.

"Plants and animals detect and respond to a range of things -- including microbes, insects, chemicals and hormones -- via cellular proteins," said Raina.

These proteins, called receptor-like kinases, or RLKs, contain a sensory area outside the cell membrane that attaches to molecules in the environment. This binding process "sends a signal inside the cell to the response domain, known as the kinase, which then turns on genes that trigger a response," he said.

By using recombinant DNA technology, scientists hope to fuse the receptor (sensing part) of these proteins to the kinase (response part) of another protein, which will make the plant respond in a visible manner to environmental stimuli, such as bio-agents.

For example, the plants could be genetically engineered to turn brown, simulating the appearance of dying tissues in a diseased plant, or a fluorescent color when brought into contact with such stimuli.

Presently the scientists are studying Arabidopsis thaliana, or mouse-ear cress, a small flowering plant in the mustard family that could be turned into a sentinel plant. The plant was chosen, in part, because its entire genetic sequence is known.

"By exposing these plants to different stimuli and looking for the response, we can determine what sensor proteins are responsible for sensing what agents," said Schultz. "The ultimate goal is to develop 'plug-and-play' kits that can be inserted into a variety of plants to act as sentinels in various situations."

A statement issued by DARPA said it could take three years to develop sentinel plants suitable for testing beyond the confines of a laboratory.

"These basic investigations will provide the DoD (Department of Defense) with entirely new ways of remotely and continuously obtaining information on chemical and biological materials via concealable devices in the air, water or soil," said DARPA. "At the end of three years, if we are successful, we would expect to have demonstrated in a laboratory setting that sentinel plants can indicate the presence of explosives."

Besides sensing the presence of chemical warfare agents or animal pathogens such as anthrax, sentinel plants could help farmers detect the presence of pests in their crops or report on the progress of fruit ripeness to optimize harvesting.

They may also be designed to detect and signal the presence of explosives in soil, which would aid in removing land mines.

"Land mines are leaky, and the soil around them contains products of TNT decomposition," said Schultz. "Seeds of plants engineered to (change color) when they detect TNT residues in soils could be sown over suspected mine fields. When we shine a laser on them, they would indicate the position of mines."


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