Aluminum-induced decrease in CO2 assimilation in citrus seedlings is unaccompanied by decreased activities of key enzymes involved in CO2 assimilation.
'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.
Chen
Li-Song
LS
College of Horticulture, Fujian Agriculture and Forestry University, Fuzhou, 350002, P.R. China. lisongchen2002@hotmail.com
Qi
Yi-Ping
YP
Smith
Brandon Rhett
BR
Liu
Xing-Hui
XH
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
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