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

G ünter D öhler and Thom as Biermann Botanisches Institut der Universität, Siesmayerstraße 70, D-60054 Frankfurt am Main, Bundesrepublik Deutschland Z. Naturforsch. 49c, 607-614 (1994); received April 25/May 30, 1994 Dedicated to Professor Hartmut Lichtenthaler on the occasion o f his 60th birthday Lipid and Fatty Acid Composition, UV-B Effects, Synchron Cultures, Marine Diatoms 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.% C 0 2. Content of protein, DNA and RNA increased linearly up to the end of the cell cycle. Pigments (chlorophyll a, chlorophyll C\ +c2, 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 phosphatidyl­ glycerol and phosphatidylcholin continued in the dark period (30% and 28%, respectively). The pattern of major fatty acids (C14:0, C16:1, C16:o, C18:1 and C2():5) varied during the cell cycle of Ditylum. Biosynthesis of acyl lipids was reduced in dependence on the UV-B dose. The most sensi­ tive lipid was digalactosyl diacylglycerol (total inhibition at 585 J m-2), whereas phosphatidyl­ cholin 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 re­ sponse of Ditylum to UV-B irradiance. The impact of UV-B resulted in an increase of unsatu­ rated long chained fatty acids (C)8, C20) and in a diminution of short chained fatty acids (C14, C)6). 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.