The events observed here may represent the tip of a mutational iceberg

Anne Britt

As expected, the light bleached the plants' green photosynthesis pigment, chlorophyll, and stunted their growth.

However, in a small but significant number of the plants, the research team also found genetic mutations had occurred in reproductive cells, meaning that the changes were handed on to the plants' descendants.

Protective layer

UV-B, which has wavelengths between 280 and 320 nanometres, has long been recognised as a hazard to human health. It will knock electrons off the DNA molecules in cells, setting off a variety of changes that can lead to cancer.

Ozone, the three-atomed oxygen molecule, is very good at absorbing UV-B.

The layer of the gas that sits about 20 to 30 km above the Earth's surface ensures most UV-B does not reach the ground.

But the reported thinning of the ozone layer, blamed on the release of some man-made gases used as propellants and refrigerants, means animals and plants could experience much higher levels of UV-B exposure in the future.

'Reporter' gene

Gerhard Ries, of the Friedrich Miescher-Institut, Basel, Switzerland, and colleagues, wanted to test the likely impact of these raised levels at a genetic level.

The team inserted a so-called "reporter" gene into tobacco plants and the familiar laboratory plant Arabidopsis thaliana.

This caused plant cells to stain blue wherever their DNA suffered changes after the radiation exposure from special lamps. In a small number of cases, the researchers also found staining in the offspring of exposed plants showing that damage had occurred in the parent's germ (reproductive) cells.

'Mutational iceberg'

Hasty conclusions should not be drawn from lab studies that may not accurately reflect real field conditions, the team reported in the journal Nature.

But they said that if the ozone layer continued to thin, as models suggested it would, at least in the short term, then the increased levels of UV-B reaching the Earth's surface could "influence the genomic stability of plant populations".

Commenting on the work, plant biologist Anne Britt, of the University of California at Davis, said much more research was needed to clarify just how much damage ultraviolet rays could cause plants.

However, she said "the events observed here may represent the tip of a mutational iceberg".