Free fatty acids, neutral and polar lipids in Hordeum vulgare exposed to long‐term fumigation with SO2

Three 9‐day‐old cultivars of Hordeum vulgare L. (Barberousse, Gerbel and Panda) were exposed to low levels of SO2 fumigation (40 ± 5 and 117 ± 20 ppb). After 48 days of treatment the seedlings were harvested for lipid analysis. In comparison to the control (plants exposed to charcoal‐filtered air), the total lipid content of fumigated seedlings declined at 40 ppb SO2 and even more so at 117 ppb in all three cultivars. A large reduction in diacylglycerols. polar lipids and free sterols was also observed after fumigations at both SO2 concentrations, whereas the treatments resulted in an increase in triacylglycerols and free fatty acids. The percentage composition of total fatty acids and that of each lipid class were changed by the fumigations. resulting in an increase in the degree of unsaturation. No changes in the percentage composition of sterols occurred in the fumigated leaves. These results suggest that even if SO2 may not directly oxidize unsaturated fatty acids at the low concentrations used here (which do not cause visible injury). it may alter lipid metabolism. This alteration. which was particularly evident in the polar lipids and sterols, could affect the functions associated with membrane stabilization, in which lipids plus sterols play a key part.