DENVER  Could airport security gardens be the wave of the future? (“Please have photo ID and boarding pass ready and walk past the rhododenrons.”) How about a defensive line of bomb-sniffing tulips in Central Park in New York, or at the local shopping mall’s indoor waterfall, or lining the streets of Baghdad?

Researchers at Colorado State University said Wednesday that they had created the platform for just such a plant-kingdom early warning system: plants that subtly change color when exposed to minute amounts of TNT in the air.

They are redesigned to drain off chlorophyll  the stuff that makes them green  from leaves, blanching to white when bomb materials are detected.

“It had to be simple, something your mom could recognize,” said June Medford, a professor of biology at Colorado State, referring to the idea of linking a plant’s chemical response to its color, visible to the naked eye.