title: Physiological characterization and light response of the CO2-concentrating mechanism in the filamentous cyanobacterium Leptolyngbya sp. CPCC 696.
abstract: We studied the interactions of the CO(2)-concentrating mechanism and variable light in the filamentous cyanobacterium Leptolyngbya sp. CPCC 696 acclimated to low light (15 μmol m(-2) s(-1) PPFD) and low inorganic carbon (50 μM Ci). Mass spectrometric and polarographic analysis revealed that mediated CO(2) uptake along with both active Na(+)-independent and Na(+)-dependent HCO(3)(-) transport, likely through Na(+)/HCO(3)(-) symport, were employed to concentrate Ci internally. Combined transport of CO(2) and HCO(3)(-) required about 30 kJ mol(-1) of energy from photosynthetic electron transport to support an intracellular Ci accumulation 550-fold greater than the external Ci. Initially, Leptolyngbya rapidly induced oxygen evolution and Ci transport to reach 40-50% of maximum values by 50 μmol m(-2) s(-1) PPFD. Thereafter, photosynthesis and Ci transport increased gradually to saturation around 1,800 μmol m(-2) s(-1) PPFD. Leptolyngbya showed a low intrinsic susceptibility to photoinhibition of oxygen evolution up to PPFD of 3,000 μmol m(-2) s(-1). Intracellular Ci accumulation showed a lag under low light but then peaked at about 500 μmol photons m(-2) s(-1) and remained high thereafter. Ci influx was accompanied by a simultaneous, light-dependent, outward flux of CO(2) and by internal CO(2)/HCO(3)(-) cycling. The high-affinity and high-capacity CCM of Leptolyngbya responded dynamically to fluctuating PPFD and used excitation energy in excess of the needs of CO(2) fixation by increasing Ci transport, accumulation and Ci cycling. This capacity may allow Leptolyngbya to tolerate periodic exposure to excess high light by consuming electron equivalents and keeping PSII open.
authors.affiliation: Department of Biology, University of Toronto, Mississauga, ON, Canada.
authors.forename: Elvin D
authors.initials: ED
authors.lastname: de Araujo
authors.forename: Jason
authors.initials: J
authors.lastname: Patel
authors.forename: Charlotte
authors.initials: C
authors.lastname: de Araujo
authors.forename: Susan P
authors.initials: SP
authors.lastname: Rogers
authors.forename: Steven M
authors.initials: SM
authors.lastname: Short
authors.forename: Douglas A
authors.initials: DA
authors.lastname: Campbell
authors.forename: George S
authors.initials: GS
authors.lastname: Espie
mesh_terms: D000064:Acclimatization / Q000187:drug effects / Q000528:radiation effects; D001639:Bicarbonates / Q000378:metabolism*; D001692:Biological Transport / Q000187:drug effects / Q000528:radiation effects; D002244:Carbon / Q000378:metabolism*; D002245:Carbon Dioxide / Q000378:metabolism*; D002247:Carbon Isotopes / Q000032:analysis; D002704:Chlorates / Q000494:pharmacology; D002734:Chlorophyll / Q000378:metabolism; D000077194:Chlorophyll A; D000458:Cyanobacteria / Q000187:drug effects / Q000302:isolation & purification / Q000502:physiology* / Q000528:radiation effects*; D004275:DNA, Ribosomal / Q000737:chemistry / Q000235:genetics; D008027:Light; D010788:Photosynthesis / Q000187:drug effects / Q000528:radiation effects*; D045332:Photosystem II Protein Complex / Q000187:drug effects / Q000528:radiation effects; D012329:RNA, Bacterial / Q000235:genetics; D012336:RNA, Ribosomal, 16S / Q000235:genetics; D013997:Time Factors
chemical_list: D001639:Bicarbonates; D002247:Carbon Isotopes; D002704:Chlorates; D004275:DNA, Ribosomal; D045332:Photosystem II Protein Complex; D012329:RNA, Bacterial; D012336:RNA, Ribosomal, 16S; D002734:Chlorophyll; D002245:Carbon Dioxide; D002244:Carbon; C032706:sodium chlorate; D000077194:Chlorophyll A