Abstract
In photosynthesis of C3 plants, CO2 molecules diffuse depending on [CO2] gradient between the ambient and mesophyll cell chloroplasts. When plants are subjected to drought stress, stomatal conductance (gs) generally decreases in response to abscisic acid (ABA) produced from the roots. However, it is little information about effects of ABA on internal conductance to CO2 diffusion from the stomatal cavities to the active sites of Rubisco (gi). Synthetic ABA (0.125-5 μM) was fed from the petioles of tobacco (Nicotiana tabacum Xanthi.), and changes in net photosynthesis rate on an area basis (A) against [CO2] in the stomatal cavities (Ci) were obtained. Simultaneously, [CO2] in the chloroplasts (Cc) was calculated from the combined measurements with chlorophyll fluorescence intensity. gi and initial slopes of A-Ci responses significantly reduced after the ABA applications although the initial slope of A-Cc did not change, suggesting that gi as well as gs is regulated by ABA.
