'Sour pummelo' ( Citrus grandis) seedlings were irrigated for 18 weeks with nutrient solution containing 0 (-Al) and 1.2 mM (+Al) AlCl 3.6H 2O * 0, 10 and 500 M sodium nitroprusside (SNP), a nitric oxide (NO) donor. Leaf malate content did not significantly change in response to SNP with or without aluminum (Al) except for an increase under 1.2 mM Al+10 M SNP, while leaf citrate content decreased with increasing SNP supply. Root malate content kept unchanging with or without Al except for an increase under 500 M SNP in the absence of Al, while SNP-treated roots had a higher or similar citrate content. Al decreased or did not affect malate content in roots and leaves, and citrate content in roots, but increased leaf citrate content. Al-treated roots and leaves displayed lower or similar activities of acid-metabolizing enzymes [phospho enolpyruvate carboxylase (PEPC), NAD-malate dehydrogenase (NAD-MDH), NADP-malic enzyme (NADP-ME), citrate synthase (CS), aconitase (ACO), NADP-isocitrate dehydrogenase (NADP-IDH), phospho enolpyruvate phosphatase (PEPP) and pyruvate kinase (PK)] except that they had higher or similar activities of NADP-ME and PK and Al-treated leaves had a higher or similar activity of PEPP. In conclusion, the OA metabolism in leaves and roots is differently affected by NO and Al interactions.
