Influence of episodes of summer O 3 on δ 5 and δ 9 fatty acids in autumnal lipids of Norway spruce [Picea abies (L.) Karst].

Current year needles from 5 yr-old Norway spruce trees, which had been exposed to either episodes of atmospheric O ₃ , or periodic mistings with simulated acid rainwater throughout three summer periods, were-analyzed for changes in molar percentages and ratios of fatty acids isolated from different lipids at the time of maximum winter hardening. No significant changes due to acidic misting were detected but significant decreases in the degree of unsaturation off both C ₁₆ and C ₁₈ , fatty acids, the molar percentage of δ ^5,9,12,15 , and the molar ratio δ ^5,9 18: 2 to δ ^9,12 18:2 in monogalactosyl diglyceride (MGDG) due to summer 0 ₃ exposures were found. Molar percentages and ratios of fatty acids did not change much in other lipids bur these changes in plastidie MGDG could be traced to a significant effect of summer O ₃ on the δ ⁴ - and δ ¹² -desaturases acting upon phosphatidyl choline (PC) in the endoplasmic reticulum. The replacement of the δ ⁶ -subset of C ₁₈ fatty acids by an equivalent δ ⁵ -series throughout was confirmed by Gas chromatography and mass spectrometry Molecular modelling also showed that the δ ⁵ forms, which resembled the δ ⁵ -isomers, are very different in shape to the δ ⁵ -series and this may account, in part, for the extremely low winter temperatures from which Norway spruce needles may recover.