Old leaves tell new leaves how many stomata to make. Carrie Straight 05.18.01 Plants get most of their nutrients through their roots, but they also bring in carbon dioxide through tiny pores on the surface of their leaves. These little pores, called stomata, open and close bringing in carbon dioxide and preventing water from evaporating out of the leaf. The number of stomata on a leaf varies with the amount of carbon dioxide in the air and the amount of light available. Leaves develop their stomata when they are very small, and probably before they can detect the carbon dioxide levels in the air. So how do these baby leaves know how many stomata to grow? Scientists from the United Kingdom predicted that mature leaves could transfer information to new leaves about carbon dioxide and light levels. To test this prediction, the scientists used the plant Arabidopsis thaliana. They placed little airtight containers over the mature leaves and maintained a constant level of carbon dioxide in the containers. The researchers kept the containers on some plants at high carbon dioxide levels and on other plants at low carbon dioxide levels. Then they looked at the new leaves that came out and counted the number of stomata per leaf area. The results from this experiment showed that the number of stomata on new leaves changed in response to the amount of carbon dioxide mature leaves were exposed to. This study is just another example of how plants communicate: in this case the plants are "talking to themselves". Lake, J. A., W. P. Quick, D. J. Beerling, and F. I. Woodward. 2001. Signals from mature to new leaves. Nature 411: 154. ©2001 The Aurora Collection, Inc. All Rights Reserved. Site Development by: Interactive Multimedia. Inc.