title: Electron transport kinetics in the diazotrophic cyanobacterium Trichodesmium spp. grown across a range of light levels.
abstract: The diazotrophic cyanobacterium Trichodesmium is a major contributor to marine nitrogen fixation. We analyzed how light acclimation influences the photophysiological performance of Trichodesmium IMS101 during exponential growth in semi-continuous nitrogen fixing cultures under light levels of 70, 150, 250, and 400 μmol photons m(-2) s(-1), across diel cycles. There were close correlations between growth rate, trichome length, particulate organic carbon and nitrogen assimilation, and cellular absorbance, which all peaked at 150 μmol photons m(-2) s(-1). Growth rate was light saturated by about 100 μmol photons m(-2) s(-1) and was photoinhibited above 150 μmol photons m(-2) s(-1). In contrast, the light level (I k) to saturate PSII electron transport (e (-) PSII(-1) s(-1)) was much higher, in the range of 450-550 μmol photons m(-2) s(-1), and increased with growth light. Growth rate correlates with the absorption cross section as well as with absorbed photons per cell, but not to electron transport per PSII; this disparity suggests that numbers of PSII in a cell, along with the energy allocation between two photosystems and the state transition mechanism underlie the changes in growth rates. The rate of state transitions after a transfer to darkness increased with growth light, indicating faster respiratory input into the intersystem electron transport chain.
authors.affiliation: State Key Laboratory of Marine Environmental Science, Xiamen University, Xiamen, Fujian, China.
authors.forename: Xiaoni
authors.initials: X
authors.lastname: Cai
authors.forename: Kunshan
authors.initials: K
authors.lastname: Gao
authors.forename: Feixue
authors.initials: F
authors.lastname: Fu
authors.forename: Douglas A
authors.initials: DA
authors.lastname: Campbell
authors.forename: John
authors.initials: J
authors.lastname: Beardall
authors.forename: David A
authors.initials: DA
authors.lastname: Hutchins
mesh_terms: D002244:Carbon / Q000378:metabolism; D002734:Chlorophyll / Q000378:metabolism; D000077194:Chlorophyll A; D000458:Cyanobacteria / Q000254:growth & development* / Q000378:metabolism / Q000528:radiation effects*; D004579:Electron Transport / Q000528:radiation effects; D007700:Kinetics; D008027:Light; D009584:Nitrogen / Q000378:metabolism; D055668:Photochemical Processes / Q000528:radiation effects; D017785:Photons; D045332:Photosystem II Protein Complex / Q000378:metabolism; D011789:Quantum Theory
chemical_list: D045332:Photosystem II Protein Complex; D002734:Chlorophyll; D002244:Carbon; D009584:Nitrogen; D000077194:Chlorophyll A