Secretion of acid phosphatase by the roots of several crop species under phosphorus-deficient conditions

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Abstract
Nine crop species (rice, wheat, soybean, lupin, azuki bean, sugar beet, tomato, cabbage and radish.) were grown in phosphorus-sufficient and phosphorus-deficient nutrient solutions. Then, the activities of acid phosphatase secreted by the roots for 24 h and of that eluted by 100 mM NaCl were investigated. Both activities of acid phosphatase increased under low phosphorus conditions in all the crop species. The activity of acid phosphatase secreted by the roots under phosphorus-deficient conditions was remarkably high in lupin and tomato, high in cabbage and radish, moderate in soybean and sugar beet, and low in wheat and azuki bean. The increased rates of activity of acid phosphatase (on a root dry weight basis) secreted under phosphorus-deficient conditions when compared with those under phosphorus-sufficient conditions ranged from 1.5 times in azuki bean to 19.9 times in lupin. The activity of acid phosphatase in the NaCl eluates was also higher in all the crop species under phosphorus-deficient conditions than that under phosphorus-sufficient conditions. Rice and lupin were grown in the nutrient solution with four phosphorus levels, and the activities of acid phosphatase secreted and eluted by 100 mM NaCl were determined during the growth. The activities of acid phosphatase in lupin were much higher than those in rice. Both activities of acid phosphatase increased with the decrease of the phosphorus concentration in the nutrient solution, and were substantially high at the initial growth stage. Significance of the secretion of acid phosphatase under phosphorus-deficient conditions was discussed.