Specific Inhibitor and Substrate Specificity of Alkaline Phosphatase Expressed in the Symbiotic Phase of the Arbuscular Mycorrhizal Fungus, Glomus etunicatum

Abstract

Specific inhibitor and substrate specificity of alkaline phosphatase in the arbuscule of Glomus etunicatum were investigated, and the possible role of this enzyme in the symbiosis was discussed. Mycor­ rhizal roots of marigold (Tagetes patula) were digest­ ed by cellulase and pectinase to separate the intrarad­ ical hyphae from the root tissue, and phosphatase activity was stained at pH 8.5 and 5.0. The activity.of alkaline phosphatase (pH 8.5) in arbuscules was m­ hibited in the presence of beryllium, whereas that of acid phosphatase (pH 5.0) was less sensitive to beryl­ lium. Specificity and effectiveness of beryllium on the alkaline phosphatase was further confirmed using fractionated (soluble and insoluble) enzyme pre­ pared from the separated hyphae. The soluble and insoluble alkaline phosphatases hydrolyzed phospho­ monoester compounds (glucose-6-phosphate, l3-glyc­ erophosphate, trehalose-6-phosphate and glucose 1- phosphate) but not pyrophosphate compounds (A-:r:P and polyphosphate) which were hydrolyzed by aCId phosphatase efficiently. The insoluble alkaline ph~s­ phatase showed high specific activity (on a protem basis) and high sensitivity to beryllium. Kinetic anal­ ysis of the insoluble alkaline phosphatase suggested the involvement of this enzyme in the sugar metab­ olism of the fungus due to lower Km values for sugar phosphate such as glucose-6-phosphate and treha­ lose-6-phosphate.