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

Phytase and acid phosphatase activities were measured in extracts from root s of 14- to 22-day old seedlings of a range of temperate pasture species th at were grown aseptically in sand culture. Phytase activity from roots of p hosphorus-(P-)-deficient Trifolium subterraneum L. was characterised. Activ ity was enhanced by 40% when extracts were passed through Sephadex G-25, an d increased by a further 20-30% with the addition of either 1 mM EDTA or 5 mM cysteine to assay solutions. The optimum temperature for phytase activit y was 50 degrees C and the optimum pH was 5.3. When compared with phosphata se activity measured in the roots of T. subterraneum, phytase activity exhi bited narrower pH and temperature optima, and was also more strongly inhibi ted by Co2+, Zn2+ and AsO42- ions. Significantly, for the five pasture spec ies examined, phytase activity was less than 5% of the total acid phosphata se activity in extracts of plant roots. Measured phytase activity ranged be tween 0.13 and 1.7 nkat g(-1) root fresh wt and was enhanced under P- defic ient relative to P- sufficient growth conditions in all of the pasture spec ies with the exception of Trifolium repens L., for which the K-m constant f or activity was 50% lower in P-deficient plants. When expressed on a root f resh wt basis, increases in phytase activity of similar to 1.25-fold were o bserved for extracts from T. subterraneum and Medicago polymorpha L., and o f up to 3.3-fold for Danthonia richardsonii A. B. Cashmore and Phalaris aqu atica 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 M NaCl.