Schroeder and colleagues discovered that in the cells surrounding the leaf stomata calcium ion "spikes"--or rapid increases and then decreases in calcium ion concentrations within cells--changed in frequency according to atmospheric carbon dioxide levels. As the carbon dioxide concentration was increased, the rapid drum roll of calcium spikes within the cells changed to a slower beat. The cells responded by reducing the size of the pores in the leaf.
In the presence of low carbon dioxide, a quick drumbeat was induced, but the stomata opened, rather than closed. Therefore, high carbon dioxide seems to prime the calcium sensors in the leaf. Jared Young, an assistant professor of biology at Mills College, who completed the study while he was a graduate student working with Schroeder at UCSD, likened this priming to removing ear plugs from someone at a rock concert.
"With very good ear plugs, someone might be able to sleep through the concert, but without the earplugs one would respond to the changes in the rhythms of the music," said Young. "Similarly, our findings suggest that carbon dioxide primes the calcium sensors to respond to the calcium spikes in the cell. Since changes in calcium concentration are used in other communication processes within cells, the need for sensor priming makes certain that the stomata don't close for inappropriate reasons."
The researchers speculate that narrowing the stomata in response to increased carbon dioxide may have an advantage for the plant.
"Even if a plant closes its pores a little in response to increasing atmospheric carbon dioxide, it would still have access to carbon dioxide," said Schroeder. "On the other hand, less water would be escaping through the pores, so the response might help plants use water more efficiently. Each plant species shows a differen
Source:University of California - San Diego