The results indicated that the synergistic or additive interactions among the components of the tripartite symbiotic association (Rhizobium-AMF-broad bean) increased plant productivity.

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SUMMARYEndomycorrhizal fungi were isolated from the root systems of Vaccinium macrocarpon Aiton, Rhododendron ponticum L., Calluna vulgaris (L.) Hull (Ericaceae) and also from a South African erica, Erica hispidula L. They were grown on a liquid medium containing inositol hexakisphosphate, fractionated into cytoplasmic, extracellular and wall-and inembrane-bound fractions and assayed for acid phosphatase. Extracellular phosphatase was demonstrated in all cultures but its activity was highest in the endophyte of E. hispidula. The wall-and membranebound acid phosphatase was the dominant fraction in the European endophytes. The extracellular acid phosphatase of high P-fed (323 mM P) mycelia of the endophyte of E. hispidula had the greatest activity (76% of total activity), whereas in low P-fed (0-1 niM P) mycelia both wall and extracellular fractions contributed almost equally to form 80 % of total activity. All the fractions contained an acid phosphatase of 173 858 MW with a broad pH optimum of 2-0 to 6-0 but a smaller enzyme of 68028 MW with a pH optimum of 65 also occurred in tbe wall fraction from low P-fed mycelia. All the enzymes were inhibited by fluoride, molybdenum, arsenate, cyanide, mercury and pbospbate but stimulated by EDTA, citi'ate and tbe ferric ion at low concentrations. A wide substrate specificity was demonstrated with maxiinum affinity for inorganic pyropbospbate, high affinities for OL-and y?-napbtbyl phosphate, pbenyl phosphate and a-glyceropbosphate and a low affinity for pbytic acid. Tbe low tnolecular weight enzyme was the only one wbicb bydrolysed organic anhydrides (ATP, ADP and AMP).