title: Substantial role for carbonic anhydrase in latitudinal variation in mesophyll conductance of Populus trichocarpa Torr. & Gray.
abstract: In Populus trichocarpa (black cottonwood), net photosynthesis (An) varies with latitude and, in northern genotypes, is supported by higher stomatal conductance (gs). We report here a parallel cline in mesophyll conductance (gm) and link this variation to carbonic anhydrase (CA) activity. Using concurrent carbon isotope discrimination and chlorophyll fluorescence methods, we examined the effects of acetazolamide, an inhibitor of CA, on gmin six representative genotypes (three from either end of the north-south cline). Acetazolamide reduced CA activity, gm, gs, chloroplast CO2concentration (Cc) and Anat normal CO2(400 μmol mol-1), the latter being reversible at saturating CO2. Absolute reductions in An, gmand CA activity were greater in northern genotypes than in southern genotypes (P < 0.025) but percent reductions were similar. In contrast, northern genotypes showed lower percent reduction in Cccompared to southern genotypes (P < 0.025). The northern genotypes had greater CA activity relative to both leaf area (two-fold) and mass (1.8-fold) (P < 0.016). The relationship between CA activity and gmwas similar whether the variation was inherent or inhibitor induced. We suggest that greater CA activity contributes to higher gmin northern P. trichocarpa genotypes, but other diffusion pathway components may also be involved.
authors.affiliation: Department of Forest and Conservation Sciences, Faculty of Forestry, University of British Columbia, Forest Sciences Centre, 2424 Main Mall, Vancouver, British Columbia, V6T 1Z4, Canada.
authors.forename: Mina
authors.initials: M
authors.lastname: Momayyezi
authors.affiliation: Department of Forest and Conservation Sciences, Faculty of Forestry, University of British Columbia, Forest Sciences Centre, 2424 Main Mall, Vancouver, British Columbia, V6T 1Z4, Canada.
authors.forename: Robert D
authors.initials: RD
authors.lastname: Guy
mesh_terms: D000086:Acetazolamide / Q000494:pharmacology; D002256:Carbonic Anhydrases / Q000378:metabolism*; D005838:Genotype; D058503:Mesophyll Cells / Q000187:drug effects / Q000378:metabolism*; D010788:Photosynthesis / Q000187:drug effects; D054046:Plant Stomata / Q000187:drug effects / Q000502:physiology; D032107:Populus / Q000187:drug effects / Q000201:enzymology* / Q000235:genetics; D019655:Quantitative Trait, Heritable
chemical_list: D002256:Carbonic Anhydrases; D000086:Acetazolamide
keywords: internal conductance; local adaptation; poplar; transfer resistance