TURGOR CHANGES IN MORCHELLA-ESCULENTA DURING TRANSLOCATION AND SCLEROTIAL FORMATION

Turgor pressure was measured during six stages of growth and pseudoscl erotial formation in Morchella esculenta indirectly (by thermocouple p sychrometer) and directly (by cell pressure probe). The fungus was gro wn on a split plate, enabling separation between mycelium growing on d efined 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 scle rotia. Direct turgor potential measurements showed that the gradient b etween the mycelium and the sclerotia increases during sclerotial deve lopment (reaching a maximum of 0.53 MPa), thereby suggesting that tran slocation 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 pr imary hyphae, which carry the stream of nutrients, to am-act transloca tion from the mycelium. Since sclerotial hyphae are too small for dire ct measurement by cell pressure probe, a psychrometer was used, reveal ing high turgor in the sclerotial tissue (1.2 MPa) during sclerotial d evelopment. Direct measurement in the primary hyphae at this time gave a value of 0.7 MPa. Taken together, these measurements indicate the p resence of a turgor gradient inside the sclerotial tissue, from the pr imary hyphae to the peripheral cells. The present study is the first t o make use of a cell pressure probe to measure turgor gradients in a f ungus during translocation followed by sclerotial morphogenesis. (C) 1 995 Academic Press, Inc.