J. Plant Physiol. 158. 367–373 (2001)  Urban & Fischer Verlag http://www.urbanfischer.de/journals/jpp Effects of CO 2 and nitrogen supply on the biochemical composition of Ulva rigida with especial emphasis on lipid class analysis Francisco J. L. Gordillo 1 * , Carlos Jiménez 2 , Madeleine Goutx 3 , Xavier Niell 2 1 Aquatic Systems Division, Agriculture and Environmental Sciences Department, Queen’s University of Belfast, Newforge Lane, BT9 5PX Belfast, UK 2 Department of Ecology, Faculty of Sciences, University of Málaga, CampusTeatinos, 29071 Málaga, Spain 3 Laboratoire de Microbiologie Marine (CNRS, E.P. 2032), Campus de Luminy, CASE 907, 13288 Marseille Cedex 9, France Received August 1, 2000 · Accepted October 5, 2000 Summary Lipid class composition was analysed in the green macroalga Ulva rigida grown under normal (350 ppm) and high (10,000 ppm) CO 2 levels, and in nitrate saturated and nitrogen limited condi- tions. A new protocol for the extraction of lipids has been defined. Culture conditions altered the fate of assimilated carbon, and significant changes were observed in protein and total lipid content in particular. A CO 2 -enriched atmosphere conditioned the effects of nitrogen limitation on lipid class composition, revealing deep qualitative changes in carbon metabolism. Triglycerides accumulated at high CO 2 and under nitrogen limitation, while chloroplast-related lipids showed an inverse response. Changes in phospholipids could be related to carbon availability as they did not respond to nitrogen limitation. The ratio sterols/acetone-mobile polar lipids followed a negative linear relation with the op- timum quantum yield for photosynthetic electron transport (F v /F m ), and was considered 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 environmental stress. Key words: carbon – CO 2 – lipids – macroalgae – nitrogen – Ulva Introduction Lipid class composition has been studied mainly in microal- gae, and the composition across several classes is quite well documented (Shifrin and Chisholm 1981). In oceanography, the analysis of the proportion of different lipid classes has been used as bioindicators of the origin and physiological * E-mail corresponding author: f.gordillo@qub.ac.uk state of the seston in a water body (e.g. Parrish 1987, Goutx 1988, Gerin and Goutx 1993). In aquaculture, the interest in lipids is strongly related to their dietary relevance for larval feeding and their possible use as alternative fuels (Volkman et al. 1989, Parrish and Wangersky 1990, Roessler 1990). Lipids have also been reported as playing a role in toxic bloom events causing fish kills (Parrish et al. 1994), and in the response of phytoplankton exposed to crude-oil extracts (Morales-Loo and Goutx 1990). All these applications have gradually increased the interest in lipid response to environ- 0176-1617/01/158/03-367 $ 15.00/0