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Plant Physiology 66:349-352 (1980)
© 1980 American Society of Plant Biologists

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Spin-label Studies of Membranes in Rye Protoplasts during Extracellular Freezing 1,2

Jas Singh and Richard W. Miller

Chemistry and Biology Research Institute, Research Branch, Agriculture Canada, Ottawa, Ontario K1A OC6 Canada

Protoplasts isolated from epicotyls of nonhardened winter rye seedlings were spin-labeled with the N-oxyl-4-4-dimethyloxazolidine derivatives of 5-ketostearic (5NS) and 16-ketostearic (16NS) acids. Spectra of the membrane-bound labels showed motional broadening with a rotational correlation time of 1.5 x 10–8 second for 5NS and 1.5 x 10–10 second for 16NS at 0 C. A procedure was developed to follow membrane changes in these protoplasts during extracellular freezing. With freezing, molecular motion of 5NS, but not of 16NS, spin probes was restricted. The increase in molecular order near the hydrated end of the membrane did not result from lowered temperatures inasmuch as no such change was observed in supercooled samples. These changes are probably due to dehydration of protoplast membranes during extracellular freezing. Similar results were obtained with multilayered egg yolk lecithin and are consistent with previous observations of changes in lecithin multibilayers during dehydration. Such alterations in membrane order might lead to irreversible membrane damage during extracellular freezing of plant cells.

1 This work is contribution No. 1121 of the Chemistry and Biology Research Institute, Agriculture Canada.

2 Part of this work was reported at the Annual Meeting of the American Society of Plant Physiologists, 1978, Blacksburg, Va.






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Copyright © 1980 by the American Society of Plant Biologists