Ozone, an important constituent of smog, has a direct effects on the genes associated with the ageing process in plants.
It has long been known that exposure to ozone speeds ageing in plants, prematurely killing them. Millions of pounds worth of crops are estimated to be lost every year.
However, the study by Jennifer Miller, assistant professor of biology at Southwestern College, Kansas, provides the first evidence that the genetic programme that controls ageing is directly affected by ozone exposure. Her work, part of her doctoral thesis at Pennsylvania State University, is published in the journal, Plant Physiology.
Dr Miller carried out tests on Arabidopsis, a so-called model plant that will soon have its genome completely sequenced.
For six hours a day days she exposed plants to low levels of ozone, but higher than found in polluted areas, for six hours a day. The leaves aged and yellowed at faster rates than that among untreated control plants.
By looking at the effect on ageing related genes in the plants every two days, she found that some were turned on earlier in the ozone-stressed plant. Another experiment revealed that ethylene production, long held to signal the timing of ageing, was not the primary signal for gene expression.
Dr Miller instead believes free radicals, thought to be responsible for ageing in people, may also be an important ageing cue in plants.
This might make it possible to develop ozone-resistant plants by selecting those that contain high levels of anti-oxidants.