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.