Radiation gives these plants the blues.

With its chlorophyll extracted, this plant becomes a potential botanical Geiger counter by displaying some of its radiation-induced mutations as blue spots. These spots record the gene-altering threat of radioactive pollution, including fallout.

A Ukrainian-Swiss research team inserted inactive bacterial genes into thale cress (Arabidopsis thaliana). When mutated, these genes make an enzyme that accepts a standard, blue chemical stain.

Working both in a laboratory and at outdoor locations around Ukraine, the scientists exposed the plants for several weeks to soil tainted with fallout from the 1986 Chernobyl reactor accident.

The greater the radiation dose, the more plant tissue accepted the blue stain, the researchers report in the November Nature Biotechnology. The increase in staining correlated with the genetic damage the researchers measured in chromosomes of onions exposed to similar levels of radiation.

The mutation rate fell, however, once radiation levels got too high (about 900 curies per square kilometer). At these exposures, the plants' cell, began dying, explains Barbara Hohn of the Friedrich Miescher Institute in Basel, Switzerland, a study author. In practice, Hohn suspects, "Pots [of plants] would be put into contaminated areas for a week or two" and then treated to reveal any spots.

This is "a handy and useful tool," says geneticist Yuri E. Dubrova of the University of Leicester in England, who studies Chernobyl's effects. Until now, he notes, "it's required literally hours with a microscope and damaging one's eyes to [tally] chromosome aberrations" due to radiation.