Secretion of acid phosphatase by the roots of crop plants under phosphorus-deficient conditions and some properties of the enzyme secreted by lupin roots

Nine crop species were grown in P-sufficient and P-deficient nutrient solutions. The activity of acid phosphatase secreted by the roots increased under P-deficient conditions in all the species examined. That of lupin increased most remarkably. The properties of the enzyme secreted by the roots of lupin was investigated. Many isozymes existed in the roots and the leaves, but only one of them was secreted into the rhizosphere in a large amount. The molecular weight of the purified enzyme secreted was estimated to be 72 KD by SDS-PAGE and 140 KD by gel filtration; it was assumed to be a homo-dimer. The iso-electric point of the enzyme was 4.7 and the pH for optimum activity 4.3. When the enzyme was mixed with aqueous solution extracted from a P-deficient soil, its activity declined to 55% of its original activity after 14 days and to 9% after 21 days.