Phytase and acid phosphatase activities in extracts from roots of temperate pasture grass and legume seedlings

Abstract

Phytase and acid phosphatase activities were measured in extracts from roots of 14- to 22- day old seedlings of a range of temperate pasture species that were grown aseptically in sand culture. Phytase activity from roots of phosphorus- (P-)-deficient Trifolium subterraneum L. was characterised. Activity was enhanced by 40% when extracts were passed through Sephadex G-25, and increased by a further 20–30% with the addition of either 1 mМ EDTA or 5 mМ cysteine to assay solutions. The optimum temperature for phytase activity was 50°C and the optimum pH was 5.3. When compared with phosphatase activity measured in the roots of T. subterraneum, phytase activity exhibited narrower pH and temperature optima, and was also more strongly inhibited by Co2+, Zn2+ and AsO42− ions. Significantly, for the five pasture species examined, phytase activity was less than 5% of the total acid phosphatase activity in extracts of plant roots. Measured phytase activity ranged between 0.13 and 1.7 nkat g–1 root fresh wt and was enhanced under P-deficient relative to P-sufficient growth conditions in all of the pasture species with the exception of Trifolium repens L., for which the Km constant for activity was 50% lower in P-deficient plants. When expressed on a root fresh wt basis, increases in phytase activity of ~1.25-fold were observed for extracts from T. subterraneum and Medicago polymorpha L., and of up to 3.3-fold for Danthonia richardsonii A.B. Cashmore and Phalaris aquatica L. Increases in acid phosphatase activity with P deficiency were less evident. Between 3.1% and 4.3% only of the total phytase activity measured in root extracts was eluted from intact roots into 0.1 М NaCl.