To elucidate the possible interaction of phosphorusinduced Al tolerance in rice by improving inorganic phosphorus metabolism and modifying cell wall polysaccharides of root tip cell walls,rice seedlings of two rice cultivars \[Feiyouduoxi 1 (Altolerant genotype) and Hongliangyou 166 (Alsensitive genotype)\]were pretreated with phosphorus (P) at concentrations of 0.5, 10 and 30 mg/L for 9 d, then treated with 50 μmol/L Al for 48 h. The results showed that total root length of both rice genotypes decreased at 50 μmol/L Al , especially in 0.5 mg/L P and Al alternate processing. Under Al toxicity stress, the malonaldehyde (MDA), ascorbic acid (ASA) and proline (Pro) contents in rice leaves of two genotypes were significantly higher in 0.5 mg/L P pretreatment than other treatments, and 10 mg/L and 30 mg/L P pretreatment significantly decreased MDA, ASA and Pro contents. These results suggested that sufficient P supply ameliorated Al damage on rice. The contents of pectin and hemicellulose 2 in root apex of Feiyouduoxi 1 were significantly lower in 30 mg/L P pretreatment than in 0.5 mg/L and 10 mg/L P pretreatment under Al toxicity, and 0.5 mg/L P pretreatment increased Feiyouduoxi 1 root acid pohosphatase(ACP) activity more significantly than 10 mg/L, 30 mg/L P and aluminum alternate processing. However, no significant differences were observed in cell wall polysaccharides components and ACP activity in Hongliangyou 166. These results suggested that Altolerant rice genotype detoxified Al via increasing the ACP activity in root tips to provide more Pi to combine with Al under P deficient condition, and decreasing the cell wall polysaccharide content to reduce Al binding sites in cell walls under P sufficient condition.
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