Phosphate efflux from intraradical hyphae of Gigaspora margarita in vitro and its implication for phosphorus translocation

The enzymatic separation of physiologically active intraradical hyphae of a rbuscular mycorrhiza (AAA) fungi from host tissue is an effective way to an alyse the physiological characteristics of intraradical hyphae. Applying this technique, first, both biomass and phosphorus (P) distributio n were quantified in the intraradical and extraradical part of Gigaspora ma rgarita colonizing onion. Second, the separated intraradical hyphae were in cubated in vitro; efflux of phosphate from the hyphae and the hyphal polyph osphate (poly P) content were determined. A substantial proportion of P in mycorrhizal roots was fungal P, while the proportion of fungal biomass to root biomass was < 2 %. Phosphate efflux an d the decrease in poly-P content in the hyphae were both enhanced by the ad dition of glucose and 2-deoxyglucose, an analogue of glucose. The degrees o f enhancement for phosphate efflux and poly-P decrease were comparable, sug gesting that P efflux from intraradical hyphae was coupled with poly-P hydr olysis. Based on these findings, the translocation of P from fungus to host was est imated in relation to the distribution of hyphal P in extraradical and intr aradical parts of the AM fungus.