Spin-Probe Studies during Freezing of Cells Isolated from Cold-Hardened and Nonhardened Winter Rye

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Abstract
Mesophyll cells isolated from cold-hardened and nonhardened winter rye (Secale cereale L. cv. Puma) were spin-labeled with the fatty-acid spin probe N-oxyl-4,4-dimethyloxazolidine 5-ketostearic acid. The probe was intercalated within the cellular membranes and changes in probe motion were followed during extracellular freezing of the cells. A correlation was observed between the lethal freezing temperatures (LT50) of the cells and the maximum hyperfine splitting value achieved by the incorporated probe. Rigid limit spectra indicated that a more ordered average packing was attained by membranes of hardened cells which survived freezing to lower temperatures.