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

Seedlings of sour pummelo (Citrus grandis) were irrigated daily for 18 weeks with nutrient solution containing four phosphorus (P) levels (50, 100, 250 and 500 mu M KH(2)PO(4)) and two aluminum (Al) levels [0 (-Al) and 1.2 mM AlCl(3)center dot 6H(2)O (+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 50 mu M P and of citrate under 50 and 100 mu M P were higher in +Al leaves than in -Al. ones, but malate concentration was tower in +Al leaves than in -Al ones under 500 mu M P. There was no difference in root malate and citrate concentrations among different P and At combinations except for an increase in malate and citrate under 50 mu M P+0 mM Al and a slight decrease in malate under 50 mu M P+1.2 mM Al. The activities of acid - metablizing 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 At 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 At interactions. (C) 2009 Elsevier GmbH. All rights reserved.