Impact of UV-B Radiation on the Lipid and Fatty Acid Composition of Synchronized Ditylum brightwellii (West) Grunow

Abstract

The marine diatom Ditylum brightwellii (West) Grunow isolated from the Baltic Sea could be synchronized by a light/dark rhythm of 6.5:17.5 h (white light intensity 8 W m -2 ) at 18 °C and 0.035 vol.% CO 2 . Content of protein, DNA and RNA increased linearly up to the end of the cell cycle. Pigments (chlorophyll a, chlorophyll c 1 + c 2 , carotenoids) and galactolipids were synthesized in the light period only. A lag phase of 2 h was observed in the biosynthesis of sulphoquinovosyl diacylglycerol and phosphatidylglycerol. Formation of phosphatidylglycerol and phosphatidylcholin continued in the dark period (30% and 28%, respectively). The pattern of major fatty acids (C 14:0 , C 16:1 , C 16:0 , C 18:1 and C 20:5 ) varied during the cell cycle of Ditylum. Biosynthesis of acyl lipids was reduced in dependence on the UV-B dose. The most sensitive lipid was digalactosyl diacylglycerol (total inhibition at 585 J m -2 ), whereas phosphatidylcholin was less affected (20% reduction). UV-B radiation during the dark period had no effect on the lipid and pigment content. Strongest inhibitory effect of UV-B on cell division, synthesis of protein, pigments, sulphoquinovosyl diacylglycerol and phosphatidylglycerol was found after UV-B radiation at the beginning of the cell cycle (0.-2. h). An exposure time at the end of the light period (4.-6. h) led to a marked damage on the synthesis of monogalactosyl diacylglycerol and phosphatidylglycerol. These findings indicate a stage-dependent response of Ditylum to UV-B irradiance. The impact of UV-B resulted in an increase of unsaturated long chained fatty acids (C 18 , C 20 ) and in a diminution of short chained fatty acids (C 14 , C 16 ). Content of ATP was not affected by UV-B radiation under the used conditions. The inhibitory effect of UV-B on synthesis of DNA, RNA, protein and acyl lipids was mainly reversible. Results were discussed with reference to UV-B damage on the enzymes involved in the biosynthesis of acyl lipids and by a reduction of available metabolites.