IN-SITU LEAF LIPID-METABOLISM IN GARDEN PEA (PISUM-SATIVUM L) EXPOSED TO MODERATELY ENHANCED LEVELS OF OZONE

The effects of ozone on the lipid metabolism of garden pea (Pisum sativum L.) was investigated in two experimental designs, To study the effects on lipid biosynthesis, pea plants were exposed for 3 d to < 5 nl l(-1) ozone or to 65 +/- 5 nl l(-1) ozone (12 h d(-1)), before labelling with [1 - C-14]acetate. To study the effects on lipid degradation, pea plants were exposed to (CO2)-C-14 for 2 h, After 3 d, when the distribution of radioactivity between lipid classes had approached the mass distribution of lipids, the plants were exposed to different levels of ozone as above, Distribution of radioactivity between lipid classes was monitored daily for 6-9 d. The results show that 65 nl l(-1) ozone caused significant alterations in lipid metabolism. The major effects of ozone fumigation of garden pea were stimulated degradation of the chloroplast lipids monogalactosyldiacylglycerol (MGDG) and digalactosyldiacylglycerol (DGDG); increased synthesis of phosphatidylethanolamine (PE); decreased synthesis of some wax components and an unknown non-polar lipid (probably associated with a light membrane fraction); and induced synthesis of another unknown non-polar lipid, associated with the cuticle and/or chloroplasts. Thus, the effects of ozone on plant lipid metabolism were widespread in the cell and indicate that ozone has direct and/or indirect effects on several membrane systems. It is noteworthy that ozone affected acyl lipids of chloroplasts and non-chloroplast membranes differently. The results of the present investigation partly differs from those obtained by other investigators. These discrepancies and the implications of the obtained results on plant membrane structure and function are discussed.