INFLUENCE OF EPISODES OF SUMMER O-3 ON DELTA(5) AND DELTA(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 mistings were detected but significant decreases in the degree of unsaturation of both C-16 and C-18 fatty acids, the molar percentage of Delta(5,9,12,15)18:4 and the molar ratio of Delta(5,9)18:2 to Delta(9,12)18:2 in monogalactosyl diglyceride (MGDG) due to summer O-3 exposures were found. Molar percentages and ratios of fatty acids did not change much in other lipids but these changes in plastidic MGDG could be traced to a significant effect of summer O-3 on the Delta(5)- and Delta(12)-desaturases acting upon phosphatidyl, choline (PC) in the endoplasmic reticulum. The replacement of the Delta(6)-subset of C-18 fatty acids by an equivalent Delta(5)-series throughout was confirmed by gas chromatography and mass spectrometry. Molecular modelling also showed that the Delta(5)-forms, which resembled the Delta(9)-isomers, are very different in shape to the Delta(6)-series and this may account, in part, for the extremely low winter temperatures from which Norway spruce needles may recover.