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The marine diatoms Bellerochea yucatanensis and Thalassiosira rotula were grown at different salinities (20/25, 35, and 40/45‰ salinity (S), respectively) under normal air (0.035 vol.% CO2). No significant variations in the percentage of gross photosynthetic products (e.g. total amino acids, sugar phosphates) were found as a function of salinity during growth. The bulk of the soluble 14C-radioactivity was detected in amino acids. 14C-labelling of glutamine increased markedly with salinity. Low salt - grown algae are characterized by enhanced amino acid pools, mainly of aspartic acid, asparagine and glutamine. It was found that the tested amino acids are not involved in osmoregulation.
14C-and 15N-Assimilation, 15N-Labelled Amino Acids, M arine D iatom s The marine diatoms Bellerochea yucatanensis and Skeletonema costatum were grown at +20 °C in 0.03 vol.% CO2 with nitrate or ammonia. The 15N -am m onia and 15N -nitrate assim ila tion and 15N -incorporation into various amino acids were studied of both diatom s during exponential growth phase in dependence of different nitrogen conditions. In all experiments the 15N -am m onia uptake was lower than the 15N -nitrate assim ilation rate up to 20-40 min photo synthesis. N itrate lim itation -cells grown in nitrate followed by growth in nitrogen-free m edium for 24 h — caused a strong 15N-label into aspartate after adding 15NH 4C1 (1 m M). In cells grown in nitrate highest enrichment of 15N was found in glutamine. Results were discussed with reference to the operating of the GS/GOGAT system and glutam ic acid dehydrogenase pathway. Photosynthetic 14CO2 fixation experiments showed a very high labelling of aspartate which was interpreted with a phosphoenolpyruvate carboxylation catalysed by phosphoenolpyruvate carb-oxykinase.
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.% CO2. Content of protein, DNA and RNA increased linearly up to the end of the cell cycle. Pigments (chlorophyll a, chlorophyll c1 + 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 phosphatidylglycerol and phosphatidylcholin continued in the dark period (30% and 28%, respectively). The pattern of major fatty acids (C14:0, C16:1, C16:0, C18:1 and C20:5) 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 (C18, C20) and in a diminution of short chained fatty acids (C14, C16). 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.