title: Aluminum-induced decrease in CO2 assimilation in citrus seedlings is unaccompanied by decreased activities of key enzymes involved in CO2 assimilation.
abstract: 'Cleopatra' tangerine (Citrus reshni Hort. ex Tanaka) seedlings were irrigated daily for 8 weeks with 1/4 strength Hoagland's nutrient solution containing 0 (control) or 2 mM aluminum (Al). Leaves from Al-treated plants had decreased CO2 assimilation and stomatal conductance, but increased intercellular CO2 concentrations compared with control leaves. On a leaf area basis, 2 mM Al increased activities of key enzymes in the Calvin cycle, including ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), NADP-glyceraldehyde-3-phosphate dehydrogenase (GAPDH), phosphoribulokinase (PRK), stromal fructose-1,6-bisphosphatase (FBPase), and a key enzyme in starch synthesis, ADP-glucose pyrophosphorylase (AGPase), compared with control leaves. Aluminum had no effect on cytosolic FBPase activity, but it decreased sucrose phosphate synthase (SPS) activity. Aluminum had no effect on area-based concentrations of carbohydrates, glucose-6-phosphate (G6P) and fructose 6-phosphate (F6P) or the G6P:F6P ratio, but it decreased the area-based concentration of 3-phosphoglycerate (PGA). Photochemical quenching coefficient (qP) and electron transport rate through PSII were greatly reduced by Al. Non-photochemical quenching coefficient (NPQ) was less affected by Al than qP and electron transport rate through PSII. We conclude that the reduced rate of CO2 assimilation in Al-treated leaves was probably caused by a combination of factors such as reduced electron transport rate through PSII, increased closure of PSII reaction centers and increased photorespiration.
authors.affiliation: College of Horticulture, Fujian Agriculture and Forestry University, Fuzhou, 350002, P.R. China. lisongchen2002@hotmail.com
authors.forename: Li-Song
authors.initials: LS
authors.lastname: Chen
authors.forename: Yi-Ping
authors.initials: YP
authors.lastname: Qi
authors.forename: Brandon Rhett
authors.initials: BR
authors.lastname: Smith
authors.forename: Xing-Hui
authors.initials: XH
authors.lastname: Liu
mesh_terms: D017607:Aluminum Compounds / Q000378:metabolism*; D002245:Carbon Dioxide; D002957:Citrus / Q000201:enzymology* / Q000502:physiology; D006597:Fructose-Bisphosphatase / Q000378:metabolism; D051599:Glucose-1-Phosphate Adenylyltransferase / Q000378:metabolism; D024601:Glyceraldehyde 3-Phosphate Dehydrogenase (NADP+) / Q000378:metabolism; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000378:metabolism; D010788:Photosynthesis / Q000187:drug effects; D018515:Plant Leaves / Q000502:physiology; D012273:Ribulose-Bisphosphate Carboxylase / Q000378:metabolism; D036226:Seedlings / Q000201:enzymology / Q000502:physiology; D014197:Trees / Q000201:enzymology* / Q000502:physiology
chemical_list: D017607:Aluminum Compounds; D002245:Carbon Dioxide; D024601:Glyceraldehyde 3-Phosphate Dehydrogenase (NADP+); D017853:Phosphotransferases (Alcohol Group Acceptor); C022390:phosphoribulokinase; D051599:Glucose-1-Phosphate Adenylyltransferase; D006597:Fructose-Bisphosphatase; D012273:Ribulose-Bisphosphate Carboxylase