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Berlin

IT IS now possible to hear plants scream. Physicists at the University of
Bonn have developed a device that listens to the stress responses of household
plants. They hope it will reveal what makes so many geranium seedlings die after
the long trip to Germany from their nurseries in the Mediterranean.

When plants are under stress, because of drought or exposure to salt, ozone
and cold, they emit ethylene gas. The experimental device, built by researchers
at Bonn’s Institute of Applied Physics, excites ethylene molecules with an
infrared laser. The laser beam is “chopped” or interrupted 2000 times per
second. Each time the beam excites the ethylene molecules, they release their
energy in the form of a tiny shock wave in the surrounding atmosphere.

These 2000-hertz vibrations are amplified with a resonance tube, similar to a
small organ pipe, then detected with a sensitive microphone. Higher levels of
ethylene produce a louder sound.

The basic technique was developed by scientists at the Catholic University of
Nijmegen in the Netherlands. But the new German device is more sensitive, and
allows scientists for the first time to study living plants for long periods
while subjecting them to stress-producing conditions.

Frank Kühnemann, one of the researchers, says that the Bonn team has so
far have measured stress levels in tobacco plants deprived of water and exposed
to high levels of ozone. Kühnemann hopes that horticulturalists will now
use the device to identify which conditions—such as vibration and
temperature—kill fragile geranium seedlings in transit.