Effects of glycerol and freezing on the appearance and arrangement of microtubules in three different systems: A freeze-substitution study.

Effects of glycerol and freezing on microtubules in three different systems viz. the ovaries of Notonecta glauca, the sperm tails of Notonecta glauca and the hyphae of the fungus Phanaerochaete velutina have been studied by means of freeze-substitution. The protofilamentous substructure of microtubules is visible in positive image whether or not the tissues are treated with glycerol prior to freezing, suggesting that it is the freezing which allows this by the weakening of hydrophobic bonding between protofilaments. Glycerol, used as a cryoprotectant, causes a re-arrangement of the microtubules which is proportional to the concentration of, and the duration of exposure to, glycerol. This rearrangement of microtubules is greater in systems where the microtubules are not inter-linked than those where microtubules have obvious intertubule linkages. Rates of cooling on freezing affected the degree of rearrangement and was less with propane than with Freon 22. Possible explanations for these effects have been discussed.