MEASUREMENT OF THERMALLY PRODUCED VOLATILE ALKANES - AN ASSAY FOR PLANT HYDROPEROXY FATTY-ACID EVALUATION

A new method designed to monitor lipid peroxidation in plants has been set up with soybean hypocotyl/radicles. The hydroperoxy fatty acids p resent in situ are converted by rapid thermal treatment (80 s and 210 J g(-1)) of the biological sample into ethane and n-pentane, which are analyzed by gas chromatography. The method has been directly calibrat ed by quantification of the hydroperoxy fatty acids by silica-phase HP LC analysis of their reduced hydroxy derivatives. Hypocotyl/radicles f rom the two soybean cultivars Argenta and Soriano were submitted to va rious chemical oxidative treatments and were analyzed for both thermal ly produced volatile alkanes and hydroperoxy fatty acid levels. Our re sults showed that ethane and n-pentane production are in both cases cl osely correlated with linolenic as well as linoleic acid hydroperoxide levels (P < 0.001). Within a given plant material, thermal conversion of both hydroperoxides into alkanes occurred with yields which were n ot dependent on the oxidative treatment. These yields are however func tions of the biological material since in Soriano and Argenta cultivar s they were around 6 and 25%, respectively. Taking into account the la st point, the alkane test cannot be used to directly quantify the abso lute lipid hydroperoxide levels of plant tissues but it is convenient to monitor the peroxidative phenomenon as it occurs. The assay is easy and rapid to perform (analysis of 50 samples per day) since no sample preparation is needed, and the low detection limit (20 pmol of alkane g(-1)) permits the analysis Of Small samples. (C) 1995 Academic Press , Inc.