Confirmation of a Link between Fungal Pigmentation, Turgor Pressure, and Pathogenicity Using a New Method of Turgor Measurement

Money, N. P., and Howard, R. J. 1996. Confirmation of a link between fungal pigmentation, turgor pressure, and pathogenicity using a new method of turgor measurement.Fungal Genetics and Biology20,217–227. A novel approach to turgor measurement has confirmed a link between melanin synthesis and appressorial turgor pressure in the rice blast fungusMagnaporthe grisea.The new technique employs a cold stage to measure the melting point of ice within individual cells. Turgor is then calculated from the difference between the melting points of intracellular ice and ice in the fluid surrounding the cell. Conidia ofM. griseawere incubated on various surfaces, and appressoria developed within 6 h. Measurements from conidia showed that wild-type and melanin-deficient strains generated the same pressures, which decreased before germ tube emergence. By contrast, wild-type appressoria generated much higher pressures than appressoria of a melanin-deficient buf−mutant. These experiments strengthen the hypothesis that melanin confers pathogenicity by facilitating the development of high pressures within appressoria.