PHOSPHATASE-ACTIVITY OF 4 ECTOMYCORRHIZAL FUNGI FOUND IN A SITKA SPRUCE JAPANESE LARCH PLANTATION IN IRELAND

Ectomycorrhizal fungi (Paxillus involutus, Suillus grevillei and two u nidentified basidiomycetes from excised Sitka spruce mycorrhizas) were isolated from stands of Sitka spruce either in monoculture or in mixt ure with Japanese larch in an Irish conifer plantation. They were grow n for 35 d on modified Melin-Norkrans liquid medium containing ferric phytate as the phosphorus source. The cultures were then separated int o wall- and membrane-bound, cytoplasmic and extracellular fractions an d assayed for phosphatase. Wall- and membrane-bound fractions containe d the most active acid phosphatase. The unidentified basidiomycetes sh owed a lower substrate affinity and higher velocity of reaction than P . involutus and S. grevillei. Wall- and membrane-bound and cytoplasmic phosphatase activities were optimum over a broad pH range (4.0-6.0). Various methods were used to release the wall-bound phosphatase and a high proportion (49-88%) appeared to be tightly held within the wall. Phosphatase released from the wall by sonication had a similar K(m) to wall-bound phosphatase but V(max) was lower. The use of a number of s ubstrates demonstrated a high affinity for inorganic pyrophosphate and sodium beta-glycerophosphate but a low phytase activity.