title: Impact of irradiance on the C allocation in the coastal marine diatom Skeletonema marinoi Sarno and Zingone.
abstract: Elemental stoichiometry and organic composition were investigated in an Adriatic strain of Skeletonema marinoi, cultured at 25 [low light (LL)] and 250 [high light (HL)]µmol photon m⁻² s⁻¹. Inorganic carbon acquisition, fixation and allocation, and silicic acid and orthophosphate uptake were also studied. The C:P ratio was below the Redfield ratio, especially at LL. In HL cells, N quota was halved, C quota was similar, silica quota was lower, growth rate and long-term net primary productivity were almost doubled, relative to LL cells. The HL:LL cell quota ratios were 6 for lipid, 0.5 for protein and 0.4 for carbohydrate. Phosphoenolpyruvate carboxylase (PEPc) and glutamine synthetase (GS) activities were unaffected by the growth irradiance; phosphoenolpyruvate carboxykinase (PEPck) was 2.5-fold more active in LL cells. This suggests that in S. marinoi, C₄ photosynthesis is unlikely, PEPc is anaplerotic and PEPck may be involved in the conversion of lipid C to carbohydrates, especially in LL cells. Because about 50% of the cost for the production of an HL cell is caused by lipid biosynthesis, we propose that the preferential allocation of C to lipid at HL takes advantage of the relatively high volume-based energy content of lipids, in an organism that reduces its size at each vegetative cell division.
authors.affiliation: Laboratorio di Fisiologia delle Alghe, Dipartimento di Scienze del Mare, Università Politecnica delle Marche, Via Brecce Bianche, 60131 Ancona, Italy.
authors.forename: Alessandra
authors.initials: A
authors.lastname: Norici
authors.forename: Anna Maria
authors.initials: AM
authors.lastname: Bazzoni
authors.forename: Alessandra
authors.initials: A
authors.lastname: Pugnetti
authors.forename: John A
authors.initials: JA
authors.lastname: Raven
authors.forename: Mario
authors.initials: M
authors.lastname: Giordano
mesh_terms: D001692:Biological Transport / Q000187:drug effects; D002241:Carbohydrates; D002244:Carbon / Q000378:metabolism* / Q000528:radiation effects; D002245:Carbon Dioxide / Q000378:metabolism; D019069:Cell Respiration; D048429:Cell Size; D002734:Chlorophyll / Q000378:metabolism; D017377:Diatoms / Q000254:growth & development / Q000502:physiology* / Q000528:radiation effects*; D005974:Glutamate-Ammonia Ligase / Q000378:metabolism / Q000528:radiation effects; D008027:Light; D008055:Lipids / Q000528:radiation effects; D046911:Macromolecular Substances / Q000378:metabolism; D009584:Nitrogen / Q000378:metabolism; D010710:Phosphates / Q000378:metabolism; D019764:Phosphoenolpyruvate Carboxykinase (ATP) / Q000378:metabolism / Q000528:radiation effects; D010730:Phosphoenolpyruvate Carboxylase / Q000378:metabolism / Q000528:radiation effects; D010788:Photosynthesis / Q000502:physiology* / Q000528:radiation effects; D012824:Silicic Acid / Q000378:metabolism; D013997:Time Factors
chemical_list: D002241:Carbohydrates; D008055:Lipids; D046911:Macromolecular Substances; D010710:Phosphates; D012824:Silicic Acid; D002734:Chlorophyll; D002245:Carbon Dioxide; D002244:Carbon; D010730:Phosphoenolpyruvate Carboxylase; D019764:Phosphoenolpyruvate Carboxykinase (ATP); D005974:Glutamate-Ammonia Ligase; D009584:Nitrogen