title: NMR 13C-isotopic enrichment experiments to study carbon-partitioning into organic solutes in the red alga Grateloupia doryphora.
abstract: The red alga Grateloupia doryphora Montagne (Howe) (Cryptonemiales, Halymeniaceae) was used as a model to investigate the effects of changes in seawater salinity on the intracellular low-molecular-weight organic compounds. Carbon-partitioning into major organic solutes was followed by 13C nuclear magnetic resonance (NMR) spectroscopy on living algae incubated in NaH13CO3-enriched seawater, and by high resolution 1H and 13C NMR experiments performed on 13C-enriched algal extracts. NMR and high performance liquid chromatography (HPLC) analyses both demonstrated that floridoside level was the most affected by changes in salinity: it rose under the hypersaline treatment and decreased under hyposaline one. Moreover, at low salinity, the high labeling of floridoside (45.3% 13C-enrichment for C1) together with its low concentrations both provided evidence of great increase in the de novo biosynthesis and turnover rate. Our experiments also demonstrated a high incorporation of photosynthetic carbon into amino acids, especially glutamate, under hypoosmotic conditions. On the other hand, isethionic acid and N-methyl-methionine sulfoxide were only partly labeled, which indicates they do not directly derive from carbon photoassimilation. In algae exposed to high salinity, elevated concentrations of floridoside coupled to a low labeling (9.4%) were observed. These results suggest that hyperosmotic conditions stimulated floridoside biosynthesis from endogen storage products rather than from carbon assimilation through photosynthesis.
authors.affiliation: Laboratoire d'Ecophysiologie et de Biotechnologie des Halophytes et des Algues Marines (LEBHAM), Université de Bretagne Occidentale-IUEM, Technopôle Brest-Iroise, 29280 Plouzané, France. christelle.simon@univ-brest.fr
authors.forename: Christelle
authors.initials: C
authors.lastname: Simon-Colin
authors.forename: Nelly
authors.initials: N
authors.lastname: Kervarec
authors.forename: Roger
authors.initials: R
authors.lastname: Pichon
authors.forename: Eric
authors.initials: E
authors.lastname: Deslandes
mesh_terms: D000596:Amino Acids / Q000737:chemistry / Q000378:metabolism; D002247:Carbon Isotopes; D005990:Glycerol / Q000031:analogs & derivatives* / Q000378:metabolism; D007513:Isethionic Acid / Q000378:metabolism; D019344:Lactic Acid / Q000378:metabolism; D019906:Nuclear Magnetic Resonance, Biomolecular / Q000379:methods*; D009994:Osmolar Concentration; D000461:Rhodophyta / Q000378:metabolism*; D012623:Seawater; D017693:Sodium Bicarbonate / Q000737:chemistry / Q000378:metabolism*; D012965:Sodium Chloride / Q000737:chemistry; D013454:Sulfoxides / Q000737:chemistry / Q000378:metabolism; D014882:Water-Electrolyte Balance / Q000502:physiology
chemical_list: C457479:2-galactopyranosylglycerol; D000596:Amino Acids; D002247:Carbon Isotopes; D013454:Sulfoxides; D019344:Lactic Acid; D012965:Sodium Chloride; D017693:Sodium Bicarbonate; D007513:Isethionic Acid; D005990:Glycerol