Shrinking Down to Size: How Plants Respond to Rising Carbon Dioxide Levels

In order to cope with rising carbon dioxide levels in the atmosphere, plants reduce the numbers of their breathing pores, according to a new study.

Biologists at the University of California, San Diego have solved the long-standing mystery behind this mechanism. As described in the journal Nature, they discovered a new genetic pathway in plants, made up of four genes from three different gene families that control the density of breathing pores - or "stomata" - in plant leaves due to higher carbon dioxide (CO2) levels.

This discovery can possibly lead to a better understanding of how plant life responds to and deals with heat stress and drought as a result of elevated levels of this greenhouse gas.

"For each carbon dioxide molecule that is incorporated into plants through photosynthesis, plants lose about 200 hundred molecules of water through their stomata," lead author Julian Schroeder explained in a press release.

"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."

Scientists, using a combination of systems biology and bioinformatic techniques, were able to determine that plants increase their expression of a key peptide hormone called Epidermal Patterning Factor-2, or EPF2, when they sense rising CO2 levels.

"The EPF2 peptide acts like a morphogen which alters stem cell character in the epidermis of growing leaves and blocks the formation of stomata at elevated CO2," explained Cawas Engineer, who was involved in the study.

By identifying EPF2 and other proteins and genes involved in this mechanism, researchers believe scientists can address a wide range of critical agricultural problems in the future, as well as develop new tools to engineer plants and crops so that they can deal with droughts and high temperatures.