Changes in organic acid metabolism differ between roots and leaves of Citrus grandis in response to phosphorus and aluminum interactions

Summary: Seedlings of sour pummelo (Citrus grandis) were irrigated daily for 18 weeks with nutrient solution containing four phosphorus (P) levels (50, 100, 250 and 500μM KH2PO4) and two aluminum (Al) levels [0 (−Al) and 1.2mM AlCl3·6H2O (+Al)]. Both malate and citrate concentrations in +Al leaves decreased with increasing P supply, but their concentrations in −Al leaves did not change in response to P supply. The concentrations of malate under 50μM P and of citrate under 50 and 100μM P were higher in +Al leaves than in −Al ones, but malate concentration was lower in +Al leaves than in −Al ones under 500μM P. There was no difference in root malate and citrate concentrations among different P and Al combinations except for an increase in malate and citrate under 50μM P+0mM Al and a slight decrease in malate under 50μM P+1.2mM Al. The activities of acid-metabolizing enzymes (citrate synthase, aconitase, phosphoenolpyruvate carboxylase, NADP-isocitrate dehydrogenase, phosphoenolpyruvate phosphatase, NAD-malate dehydrogenase, NADP-malic enzyme and pyruvate kinase) in most cases were less affected by P and Al interactions in roots compared to the leaves. Our results support the hypothesis that changes in organic acid metabolism differ between roots and leaves of C. grandis in response to P and Al interactions. [Copyright &y& Elsevier]