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 wi th simulated acid rainwater throughout three summer periods, were anal yzed for changes in molar percentages and ratios of fatty acids isolat ed from different lipids at the time of maximum winter hardening. No s ignificant changes due to acidic mistings were detected but significan t 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 rati o 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 ra tios of fatty acids did not change much in other lipids but these chan ges in plastidic MGDG could be traced to a significant effect of summe r O-3 on the Delta(5)- and Delta(12)-desaturases acting upon phosphati dyl, 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 resembl ed the Delta(9)-isomers, are very different in shape to the Delta(6)-s eries and this may account, in part, for the extremely low winter temp eratures from which Norway spruce needles may recover.