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.
ELECTRON HISTOCHEMICAL LOCALIZATION OF ACID PHOSPHATASE ACTIVITY IN THE SMALL INTESTINE OF MOUSE
