Effect of Aluminum on Uptake & Translocation of Phosphorus by Perennial Ryegrass

Low levels of aluminum (1.85 x 10/sup -4/ M) increased the total content and concentration of stable phosphorus in both roots and shoots of 8 week old perennial ryegrass plants. High levels (18.5 x 10/sup -4/ M) depressed the total phosphorus but increased the concentration, a reflection of the overall reduction in growth. Low levels of aluminum whether given as a pretreatment during the growth period or during the 4-hour uptake period greatly increased the short term uptake of P/sup 32/. Higher levels of aluminum reduced the uptake. Similar patterns were obtained for both 4.5 x 10/sup -4/ M and 22.5 x 10/sup -4/ M P uptake solutions. Potassium cyanide caused a marked inhibition of aluminuminduced phosphorus uptake into the root. In the absence of aluminum, 5 x 10/sup -4/ M 2,4-dinitrophenol increased transport to the shoots, but with aluminum there was no increase. Manganese sulfate stimulated phosphorus translocation to the shoots. It is concluded that the aluminuminduced increase in phosphate uptake is largely a metabolic process, although precipitation effects on the root cannot be ruled out. A mechanism based on the known stimulation by aluminum of the reduction of cytochrome is postulated for the increase in uptake. On themore » basis of the effect of 2,4-dinitrophenol, it is suggested that subsequent to the uptake process, phosphorus is bound by aluminum within the plant, thus causing the symptoms of phosphorus deficiency characteristic of aluminum toxicity.« less