No fragrance, no interest

When a flower stops smelling like one,  pollination is in jeopardy. And pollution is to blame, writes Sumana Narayanan

THE attractiveness of a flower diminishes when it does not emit a fragrance. And not just we humans but insects, too, stop taking an interest in such a flower. Researchers from the University of Virginia, USA, have sounded a warning that the fragrance in flowers may be short-lived. The cause, they say, is air pollution. This is crucial because both colour and fragrance attract insects towards flowers, thus helping pollination. Their study shows that increasing levels of nitrogen oxides in the air react with and degrade hydrocarbons responsible for fragrance in flowers. Hydrocarbons react easily with nitrogen oxides (NO and NO2) in the air to form ozone (O3).

This restricts the fragrance from travelling long distances — about 200 metres — thus making it difficult for insects to find flowers. Simulation studies showed that at pre-industrial levels of air pollution, the fragrance of a flower could travel several kilometres. The hydrocarbons break down even before they can be carried away by the wind, the researchers say in the paper published in the March 2008 issue of the Atmospheric Environment. The researchers used mathematical models to understand how common fragrance hydrocarbons — linalool, myrcene and ocimene — disperse in the air.

In highly polluted conditions, 75 per cent of the fragrance gets killed within 200-300 metres of the source plant. This could mean that insects will take longer to find isolated flower patches and so their efficiency as pollinators could be reduced. Besides, the ability of insects to differentiate between scents could also be affected since flower scents are a combination of various hydrocarbons, the researchers said in the paper.  “Pollution affects all aspects of plant biology, so it is not surprising that a flower’s fragrance is also altered. This could affect reproductive success in small populations. It could also lead to an increase in the loss of genetic variation due to inbreeding,” says AK Bhatnagar, head of the Department of Botany, Delhi University. Yet another new study delves into what causes diseases such as cancer, diabetes or obesity. It’s possible that genes are the cause. The other probability is that these are related to one’s lifestyle. Popularly known as the nature versus nurture debate, it was believed there was a balance between the two. But the new study shows that external environment (nurture) has a greater effect than genes (nature).

Several epidemiological studies on incidence of diseases are being carried out to find a conclusive answer to how genes and the external environment react with each other.

Researchers from Princeton University used yeast for their experiment. Yeast is a good model to show how genes work in human beings and give the opportunity to study thousands of gene expression patterns. The researchers used two genetically different strains of yeast from two different environments: one from the laboratory and the other from a vineyard.

The study says that, just like in humans, a balance exists between genes and environment in yeast, which determines its traits. The interesting part is that the expression of many genes in yeast is under the control of other genes. These other genes are almost always affected by the external environment. The study was published in PLoS Biology.