Stomatal physiology in intact leaves
We are studying how stomatal aperture is regulated in relation to changes in water supply and evaporative demand, and changes in CO2 supply and demand in the mesophyll. Collectively, these regulatory processes produce varying degrees of homeostasis in two state variables: leaf water potential and intercellular CO2 concentration. Leaf water potential is not well defined, because it can vary greatly among tissues and even nearby cells within leaves, and evidence suggests these gradients can be large and dynamic. Likewise, chloroplastic CO2 concentration -- which is relevant to photosynthesis -- can differ strongly from intercellular CO2 concentration due to internal resistance, also now understood to be large and dynamic.

Various mechanisms have been hypothesised for the stomatal responses that produce quasi-homeostasis. These hypotheses depend sensitively on exactly where water status and CO2 concentration are sensed. We are carrying out research designed to differentiate among these hypotheses, using traditional whole-leaf techniques such as gas exchange and cell pressure probing. All of this work is informed by, and in turn informs, mathematical models of leaf function.

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