Do Stomata Respond to CO2 Concentrations Other than Intercellular?

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Abstract
Most studies on stomatal responses to CO2 assume that guard cells respond only to intercellular CO2 concentration and are insensitive to the CO2 concentrations in the pore and outside the leaf. If stomata are sensitive to the CO2 concentration at the surface of the leaf or in the stomatal pore, the stomatal response to intercellular CO2 concentration will be incorrect for a `normally' operating leaf (where ambient CO2 concentration is a constant). In this study asymmetric CO2 concentrations for the two surfaces of amphistomatous leaves were used to vary intercellular and leaf surface CO2 concentrations independently in Xanthium strumarium L. and Helianthus annuus L. The response of stomata to intercellular CO2 concentration when the concentration at the leaf surface was held constant was found to be the same as the response when the surface concentration was varied. In addition, stomata did not respond to changes in leaf surface CO2 concentration when the intercellular concentration for that surface was held constant. It is concluded that stomata respond to intercellular CO2 concentration and are insensitive to the CO2 concentration at the surface of the leaf and in the stomatal pore.

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