ESTIMATION OF VACUOLAR PH IN ACTIVELY GROWING HYPHAE OF THE FUNGUS PISOLITHUS-TINCTORIUS

The pH of vacuoles in tip cells of growing hyphae of a mycorrhizal fun gus, Pisolithus tinctorius, was estimated by dual-wavelength microspec trofluorometry of 6-carboxyfluorescein. The vacuoles were found to hav e a modal pH of 7.0-7.5 and a pH range of 4.3-7.5. Vacuoles in penulti mate cells tended to be more acid, with a modal group pH 5.5-6.0, alth ough the range was similar at pH 4.8-7.2. The findings are discussed i n relation to endocytosis and ageing of vacuoles in P. tinctorius.