Two Brazilian wheat varieties (Triticum aestivum L., varieties IAC-5 and Jupateco) were grown in solution culture with three concentrations of P (1, 5 and 20 μg ml-1) and no Al, then transferred to three concentrations of Al (0, 2.5 and 12.5 μg ml-1) and no P and afterwards returned to the first solutions. In the first growth period the tolerant variety IAC-5 absorbed and translocated more P to the shoots than the sensitive one. In the second period A1 restricted both root growth and the translocation of P from root to shoot, and led to movement of P from shoots to roots in plants with low P contents, the sensitive variety again being most affected. The amount of P translocated to the roots was approximately equal to the increase in isotopically-exchangeable P in the roots. In the third period, root P taken up in the first period was translocated to the shoots in amounts approximately equal to the total exchangeable P in the roots, along with freshly absorbed P. After the second period tissue was ground and filtered to give a filtrate (predominantly cell contents) and a residue (predominantly cell walls). The A1: P ratio (μmol g-1 dry matter) in the contents was about 1:7, and in the walls it was 1:2. The latter value may indicate the composition of aluminium phosphate precipitated in the walls. Tolerance of soil acidity is associated with the ability of roots to translocate P to shoots in the presence of A1 and may also depend on the ability to move P down to roots growing in acid subsoils.
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