Surface phosphatase activities on roots of Pakistani wheat cultivars

A study of the surface phosphatase activity of different wheat cuhivar roots was carried out, using two substrates, p-nitrophenyl phosphate (pNPP) and 4- methylumbellferyl phosphate (4-MUP), and different pH values ranging from 3 to 10.0. Seedlings of the wheat cultivars, Indus-66, Jauhar-78 and Pavan, were grown in Hoagland solution under P-sufficient and P-limited conditions, each for 5, 10 and 15-days. The optimum pH for phosphatase activity differed in the different cultivars, but was always acidic, ranging from pH 4.0 to 6.0.P-limited plants showed greater phosphatase activity than P-suflficient ones with both substrates. Phosphatase activity increased within the first 5-day interval of the plants being deprived of phosphorus, and reached a peak by the 10-day age. In 5-day old plants, cv Pavan showed highest PMEase activity (0.06 µmol mg d.wt(^-1) h(^-1) at pH 5.0); however in cv Indus-66 (0.08 µmol mg d. wt (^-1) h(^-1)) and cv Jauhar-78 (0.07 µmol mg d. wt(^-1) h(^-1)) the highest activity was in 10-day old plants at pH 4.5 and 6.0, respectively. This occurred with both substrates. The pH optima of P-sufficient and P- limited plants were similar. As root surface phosphatase activity is an adaptive response, this could be used to distinguish cultivars suitable for growing in low inorganic phosphate fertility situations.