Spin label electron paramagnetic resonance study in thylakoid membranes from a new herbicide-resistant D1 mutant from soybean cell cultures deficientin fatty acid desaturation

The effect of fatty acid desaturation on lipid fluidity in thylakoid membra nes isolated from the STR7 mutant was investigated by electron paramagnetic resonance (EPR) using spin label probes. The spectra of both 5- and 16-n-d oxylstearic acid probes were measured as a function of the temperature betw een 10 and 305 K and compared to those of the wild type. This complete ther mal evolution provides a wider picture of the dynamics. The spectra of the 5-n-doxylstearic acid probe as well as their temperature evolution were ide ntical in both STR7 mutant and wild type thylakoids. However, differences w ere found with the 16-n-doxylstearic acid probe at temperatures between 230 and 305 K. The differences in the thermal evolution of the EPR spectra can be interpreted as a 5-10 K shift toward higher temperatures of the probe m otional rates in the STR7 mutant as compared with that in the wild type. At temperatures below 230 K no differences were observed. The results indicat ed that the lipid motion in the outermost region of the thylakoids is the s ame in the STR7 mutant as in the wild type while the fluidity in the inner region of the STR7 mutant membrane decreases. Our data point out a picture of the STR7 thylakoid membrane in which the lipid motion is slower most pro bably as a consequence of fatty acid desaturation deficiency. (C) 2001 Else vier Science B.V. All rights reserved.