Effects of CO2 and nitrogen supply on the biochemical composition of Ulva rigida with especial emphasis on lipid class analysis

Lipid class composition was analysed in the green macroalga Ulva rigida gro wn under normal (350 ppm) and high (10,000 ppm) CO2 levels, and in nitrate saturated and nitrogen limited conditions. A new protocol for the extractio n of lipids has been defined. Culture conditions altered the fate of assimi lated carbon, and significant changes were observed in protein and total li pid content in particular. A CO2-enriched atmosphere conditioned the effect s of nitrogen limitation on lipid class composition, revealing deep qualita tive changes in carbon metabolism. Triglycerides accumulated at high CO2 an d under nitrogen limitation, while chloroplast-related lipids showed an inv erse response. Changes in phospholipids could be related to carbon availabi lity as they did not respond to nitrogen limitation. The ratio sterols/acet one-mobile polar lipids followed a negative linear relation with the optimu m quantum yield for photosynthetic electron transport (F-v/F-m), and was co nsidered as an index of the "light status" of the cell. The specificity of the response of lipid classes to growth conditions in U. rigida emphasizes the potential role of lipid class analyses as a diagnostic tool for environ mental stress.