Development of a phosphatase activity assay using excised plant roots

Abstract

Root phosphatase mediated mineralisation of organic phosphorus (P) can affect P availability in agricultural and forest landscapes. Phosphatases hydrolyse organic P into inorganic P that can be taken up by plants. We developed a method to determine mineralisable organic P by phosphatases exuded by excised live roots/microbial systems. We used excised greenhouse- and field-grown roots with para-nitrophenylphosphate, glucose-1-phosphate and phytic acid as sources of organic P. Experimental variables were analysed including linearity of the reaction, presence of inorganic P, organic P exuded from roots, possible abiotic degradation of organic P, and background inorganic/organic P. Organic P mineralisation by root–phosphatase complexes was found to be linear through 6 h. Phosphorus contaminants into the system were found to be within 10% of mineralised organic P. We used this technique to answer questions about organic P bioavailability, including effect of organic P sources, plant species, plant variety, plant stress and root conditions. Overall, this method was sensitive to organic P source and plant stress of greenhouse and field-grown roots, plant species and root physiological conditions. Unlike other methods used to determine phosphatase activity, this method is not limited by lengthy preparation to develop model plants, nor is there any restriction on the choice of organic P or plant species. Our results suggest that this is an attractive method for determining organic P mineralisation specificity among and within plant species, and it can be easily integrated into routine laboratory analyses.