TURGOR CHANGES IN MORCHELLA-ESCULENTA DURING TRANSLOCATION AND SCLEROTIAL FORMATION

Turgor pressure was measured during six stages of growth and pseudosclerotial formation in Morchella esculenta indirectly (by thermocouple psychrometer) and directly (by cell pressure probe). The fungus was grown on a split plate, enabling separation between mycelium growing on defined medium (water potential -0.5 MPa) and sclerotia which formed on glucose noble agar (water potential -2.1 MPa). Under these conditions, nutrients were translocated from the mycelium to the developing sclerotia. Direct turgor potential measurements showed that the gradient between the mycelium and the sclerotia increases during sclerotial development (reaching a maximum of 0.53 MPa), thereby suggesting that translocation is a turgor-driven mass flow. During sclerotial development, the turgor potential in the peripheral tips of the sclerotial hyphae must be high enough to bring about the growth of the numerous hyphae, which comprise the sclerotium, and simultaneously low enough in the primary hyphae, which carry the stream of nutrients, to am-act translocation from the mycelium. Since sclerotial hyphae are too small for direct measurement by cell pressure probe, a psychrometer was used, revealing high turgor in the sclerotial tissue (1.2 MPa) during sclerotial development. Direct measurement in the primary hyphae at this time gave a value of 0.7 MPa. Taken together, these measurements indicate the presence of a turgor gradient inside the sclerotial tissue, from the primary hyphae to the peripheral cells. The present study is the first to make use of a cell pressure probe to measure turgor gradients in a fungus during translocation followed by sclerotial morphogenesis. (C) 1995 Academic Press, Inc.