How plants respond to elevated CO2 levels

Researchers have solved a long-standing mystery concerning the way plants reduce the numbers of their breathing pores in response to rising carbon dioxide levels in the atmosphere.

A genetic pathway in plants, made up of four genes from three different gene families control the density of breathing pores - or "stomata" in plant leaves - in response to elevated CO2 levels, the researchers discovered.

"For each carbon dioxide molecule that is incorporated into plants through photosynthesis, plants lose about 20,000 molecules of water through their stomata," said Julian Schroeder, a professor of biology at University of California, San Diego in the US.

Because elevated CO2 reduces the density of stomatal pores in leaves, this is, at first sight beneficial for plants as they would lose less water.

"However, the reduction in the numbers of stomatal pores decreases the ability of plants to cool their leaves during a heat wave via water evaporation. Less evaporation adds to heat stress in plants, which ultimately affects crop yield," Schroeder said.

Working on a tiny mustard plant called Arabidopsis, which is used as a genetic model and shares many of the same genes as other plants and crops, the researchers discovered that the proteins encoded by the four genes they discovered repress the development of stomata at elevated CO2 levels.

Using a combination of systems biology and bioinformatic techniques, the scientists cleverly isolated proteins, which, when mutated, abolished the plant's ability to respond to CO2 stress.

When plants sense atmospheric CO2 levels rising, they increase their expression of a key peptide hormone called Epidermal Patterning Factor-2, EPF2, said Cawas Engineer, a postdoctoral scientist in Schroeder's laboratory.

The discovery could provide agricultural scientists with new tools to engineer crops that can deal with droughts and high temperatures.

The findings appeared online in the journal Nature.