Freeze-induced phase transitions in the plasma membrane of isolated protoplasts |
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Authors: | Kaarina Pihakaski Peter L Steponkus |
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Institution: | Dept of Biology, Univ. of Turku. SF-20500 Turku, Finland;Dept of Agronomy, Cornell Univ., Ithaca, New York 14853. U.S.A. |
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Abstract: | Protoplasts were enzymically isolated from 2-week-old non-acclimated rye ( Secale cereale L. cv. Puma) seedlings. They were resuspended in isotonic sorbitol with different concentrations (0–10%) of dimethyl sulfoxide (DMSO). The survival of the protoplasts frozen in isotonic sorbitol solutions declined at temperatures below the freezing point with the LT50 being -8°C. Addition of DMSO to the osmoticum increased survival at freezing temperatures. The optimum concentration of DMSO was 4% and lowered the LT50 to -19°C. Freeze-fracture studies of the plasma membrane revealed aparticulate lipid lamellae at -4°C, but the first appearance of lateral phase separations, striations and inverted cylindrical micelles (hexagonal11-type structures) occurred at -6°C. At lower temperatures, -8 and -10°C, the occurrence of nonbilayer structures became more common. The addition of DMSO decreased the incidence of the ultrastructural changes. With 2 or 4% DMSO, non-bilayer structures were not observed at temperatures above -10°C. Instead, striations and H11-type structures were observed at - 15 and -20°C. |
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Keywords: | Inverted cylindrical micelles DMSO freeze-fracture electron microscopy Secale cereale |
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