title: Effects of nitrogen availability on pigmentation and carbon assimilation in the cyanobacterium Synechococcus sp. strain SH-94-5.
abstract: Because pigments of phototrophs can be involved either in photosynthesis or photoprotection, pigmentation changes in response to nutrient availability can affect how cells interact with their solar environment. We investigated the impact of nitrogen availability both on pigmentation of the cyanobacterium Synechococcus sp. strain SH-94-5 and on carbon assimilation by this strain in the presence or absence of UV radiation. Pigmentation changes in strain SH-94-5 due to ammonium exhaustion included phycobiliprotein degradation, an exponential decline in chlorophyll a content, and a net increase in beta-carotene. Following its replenishment, ammonium stimulated non-photosynthetic carbon assimilation for several hours prior to the resumption of photosynthesis and growth. Carbon fixation during this lag phase was concurrent with the metabolism of glycogen reserves, and it is likely that inorganic carbon was incorporated into glycogen-derived carbon skeletons primarily for amino acid synthesis. In contrast, carbon fixation was almost exclusively photosynthetic during exponential growth. UV-A radiation (320-400 nm) inhibited photosynthetic but not non-photosynthetic carbon assimilation. Only growing cells were inhibited, and the disappearance of inhibition following nitrogen depletion appeared to result from the reduction of cellular photosensitizing targets below a threshold level rather than from the inactivation of photosynthesis.
authors.affiliation: Department of Biology, University of Oregon, Eugene, Oregon 97403, USA, srmille4@unity.ncsu.edu
authors.forename: Scott R
authors.initials: SR
authors.lastname: Miller
authors.forename: Miriam
authors.initials: M
authors.lastname: Martin
authors.forename: Janeene
authors.initials: J
authors.lastname: Touchton
authors.forename: Richard W
authors.initials: RW
authors.lastname: Castenholz
mesh_terms: D002244:Carbon / Q000378:metabolism*; D002734:Chlorophyll / Q000378:metabolism; D000458:Cyanobacteria / Q000235:genetics / Q000254:growth & development / Q000378:metabolism* / Q000528:radiation effects; D009584:Nitrogen / Q000378:metabolism*; D010788:Photosynthesis / Q000528:radiation effects; D010860:Pigments, Biological / Q000378:metabolism*; D014466:Ultraviolet Rays; D019207:beta Carotene / Q000378:metabolism
chemical_list: D010860:Pigments, Biological; D019207:beta Carotene; D002734:Chlorophyll; D002244:Carbon; D009584:Nitrogen