Abstract
There are some papers reporting that the conductance for CO2 diffusion from intercellular air space to the site of carboxylation (gm) decreases when plants are exposed to drought. However, plants close their stomata and decrease stomatal conductance (gs) when they are exposed to drought. Moreover, they tend to close in patchy. Because accurate estimation of CO2 concentration in the intercellular air space (Ci) is prerequisite for the gm measurement, the Ci and gm values so far obtained under drought conditions are not reliable.
We have tested to use an ABA-deficient mutant, Nicotiana plumbaginifolia (aba1), to avoid inaccurate gm estimation due to stomatal closure. As an index of drought stress, we set saturating soil water content as 100%. When it decreased to 20%, gs decreased significantly in WT, whereas gs value was still high in aba1. Therefore, we use this mutant for the experiment following change in gm when the plants are exposed to drought and recovered from it. We are also measuring the amount of aquaporin, chloroplast surface area exposed to intercellular air space (Sc) and the activity of carbonic anhydrase to elucidate mechanisms underlying the changes in gm.
