Abstract
In C3 photosynthesis plants, [CO2] in the chloroplasts (Cc) is often lower than half the ambient [CO2]. Such reduction of Cc is attributed to CO2 gas diffusion conductance from stomatal cavities to the chloroplasts (gm). Some recent studies have suggested that plasma-membrane-type aquaporin contents have positive relationships with gm using transgenic plants. Drought stress generally decreases gm. However, it is uncertain that aquaporin contents explain the change in gm. Tobacco (Nicotiana tabacum) plants were intermittently irrigated (stressed) while some were constantly irrigated (control). gm in stressed plants was about one-third that in control. gm had a positive relationship against area-based leaf nitrogen content in both treatments. A significant level of PIP1-type aquaporin was not found, and PIP2-type aquaporin content was slightly lager in stressed plants than in control. These results suggest that the reduction of gm in response to drought is independent of leaf aquaporin contents.
