LAMELLAR TO HEXAGONAL-II PHASE-TRANSITIONS IN TONOPLASTS OF MUSHROOM HYPHAE CAUSED BY MECHANICAL-STRESS RESULTING FROM THE FORMATION OF EXTRACELLULAR ICE CRYSTALS

Slow freezing produced lamellar to hexagonal II (L to HII) phase transitions in tonoplasts of tertiary hyphae, which comprise the fruiting bodies of several species of Basidiomycetes. Neither dehydration by osmotic manipulation in a 5.37 osmolal solution nor temperature reduction by supercooling (at -10 °C) produced L to HII phase transitions in the tonoplast. The freezing temperatures at which L to HII phase transitions were formed ranged from -3 to -30 °C in the different species. Within the same species, the temperatures corresponded closely to those at which severe cellular deformation causing intramembrane particle aggregation in the plasma membranes took place. From previous papers (S. Fujikawa and K. Miura, Cryobiology 23, 371-382, 1986; S. Fujikawa, J. Electron Microsc. 39, 80-85, 1990), it is suggested that severe cellular deformation was caused by mechanical stress produced by the formation of extracellular ice crystals during slow freezing. From these results, it was concluded that the L to HII phase transitions in tonoplasts were produced by interbilayer events caused by mechanical stress resulting from the formation of extracellular ice crystals during slow freezing. © 1991.