The changes act as a defence mechanism that prevents the trees' genome from being destabilised by radiation. The explosion of one of Chernobyl's reactors showered trees in the surrounding area with a huge amount of radioactivity. Scots pines (Pinus silvestris) that received the biggest radiation doses- in excess of 60 grays- died, turned brown and became known as "the red forest". But those exposed to smaller doses survived, suggesting they may have found ways of tolerating the radiation.
To test the theory, Olga Kovalchuk from the University of Lethbridge in Alberta, Canada, with Andrey Arkhipov and Nikolai Kuchma from the Chernobyl Centre in Ukraine conducted long-term experiments in which they planted uncontaminated Scots pine seeds in the highly contaminated soil where Chernobyl's radioactive debris was buried.
When the trees were 10 years old, they measured their levels of methylation, the process in which methyl groups are added to DNA. In plants, it regulates gene expression and protects essential genes from damage. In a forthcoming paper in the journal Mutation Research, the scientists report that there was 30 per cent more methylation in the trees grown in contaminated ground than in similar trees grown in clean soil.
In another experiment, they found increased methylation in 40-year-old trees that had survived Chernobyl's radiation. Methylation is"a response to stress that prevents genomic instability and enables survival in an extremely hostile environment", Kovalchuk told New Scientist.
John Stather, a senior scientist with the National Radiological Protection Board in the UK, says the findings are of "considerable interest". International investigations into how best to protect plants and animals from the harmful effects of radiation are already under way, he says (New Scientist, 12 April, p 10).
New Scientist issue: 6th September 2003
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