Sour pummelo ( Citrus grandis) seedlings were irrigated with nutrient solution containing four boron concentrations ( i.e., 2.5, 10, 25 and 50 M H 3BO 3) and two aluminum concentrations [ i.e., 0 (-Al) and 1.2 mM AlCl 3 . 6 H 2O (+Al)]. It was found that B did not affect, but Al increased, the Al content in the roots. The Al and citrate contents in the -Al leaves either did not change or slightly increased with increasing B concentration. On the other hand, the Al and citrate contents in the +Al leaves rapidly decreased as B concentration increased from 2.5 to 50 M, then decreased at the highest B concentration. The Al and citrate contents were higher in the +Al than in the -Al leaves, except for at 25 M B when they were similar. The leaf malate content did not change in response to B or Al, except for an increase in the +Al leaves and a decrease in the -Al leaves at 2.5 M B. Similarly, the root malate and citrate contents did not change in response to B with or without Al, except for a decrease in the malate and citrate contents in the +Al roots at 50 M B and an increase in the citrate content in the -Al roots at 50 M B. The activities of acid-metabolizing enzymes were less affected by B-Al interactions in the roots than in the leaves.
