Heterogeneous inhibition of photosynthesis over the leaf surface of Rosa rubiginosa L. during water stress and abscisic acid treatment:: induction of a metabolic component by limitation of CO2 diffusion

The contribution of changes in stoma tal conductance and metabolism in determining heterogeneous photosynthesis inhibition during dehydration and abscisic acid (ABA) feeding was investigated using detached leaves of Rosa rubiginosa L. The steady-state and maximal rates of electron transport under a transient high CO2 concentration were monitored using chlorophyll fluorescence imaging. The decrease in electron transport rate induced by dehydration and ABA treatment almost reverted to the control rate under transient high CO2 availability. Therefore, inhibition of photosynthesis was mainly mediated through stomatal closure. However, since reversion was not complete, a metabolic inhibition was also identified as a decrease in the maximal electron transport rate driven by carboxylation. Under dehydration or ABA feeding, as under low ambient CO2 treatment, in 21% or 0.4% O-2, the lower the steady-state electron transport was, the lower was the maximal electron transport rate during transient high CO2 availability. We conclude that low CO2 availability reduced the capacity of ribulose-1,5-bisphosphate carboxylase-oxygenase (Rubisco) to drive electron transport. The potential contribution of Rubisco deactivation mediated by stomatal closure is discussed.