title: Elevated CO2 causes changes in the photosynthetic apparatus of a toxic cyanobacterium, Cylindrospermopsis raciborskii.
abstract: We studied the physiological acclimation of growth, photosynthesis and CO2-concentrating mechanism (CCM) in Cylindrospermopsis raciborskii exposed to low (present day; L-CO2) and high (1300ppm; H-CO2) pCO2. Results showed that under H-CO2 the cell specific division rate (μc) was higher and the CO2- and light-saturated photosynthetic rates (Vmax and Pmax) doubled. The cells' photosynthetic affinity for CO2 (K0.5CO2) was halved compared to L-CO2 cultures. However, no significant differences were found in dark respiration rates (Rd), pigment composition and light harvesting efficiency (α). In H-CO2 cells, non-photochemical quenching (NPQ), associated with state transitions of the electron transport chain (ETC), was negligible. Simultaneously, a reorganisation of PSII features including antenna connectivity (JconPSIIα), heterogeneity (PSIIα/β) and effective absorption cross sectional area (σPSIIα/β) was observed. In relation to different activities of the CCM, our findings suggest that for cells grown under H-CO2: (1) there is down-regulation of CCM activity; (2) the ability of cells to use the harvested light energy is altered; (3) the occurrence of state transitions is likely to be associated with changes of electron flow (cyclic vs linear) through the ETC; (4) changes in PSII characteristics are important in regulating state transitions.
authors.affiliation: School of Biological Science, Monash University, Clayton 3800, Victoria, Australia. Electronic address: mattia.pierangelini@monash.edu.
authors.forename: Mattia
authors.initials: M
authors.lastname: Pierangelini
authors.affiliation: School of Biological Science, Monash University, Clayton 3800, Victoria, Australia; CSIRO Marine and Atmospheric Research, Hobart, Tasmania, Australia.
authors.forename: Slobodanka
authors.initials: S
authors.lastname: Stojkovic
authors.affiliation: School of Biological Science, Monash University, Clayton 3800, Victoria, Australia; Seqwater, PO Box 16146, City East 4002, Queensland, Australia.
authors.forename: Philip T
authors.initials: PT
authors.lastname: Orr
authors.affiliation: School of Biological Science, Monash University, Clayton 3800, Victoria, Australia.
authors.forename: John
authors.initials: J
authors.lastname: Beardall
mesh_terms: D002244:Carbon / Q000494:pharmacology; D002245:Carbon Dioxide / Q000494:pharmacology*; D002455:Cell Division / Q000187:drug effects; D019069:Cell Respiration / Q000187:drug effects; D046891:Cylindrospermopsis / Q000166:cytology / Q000187:drug effects* / Q000502:physiology*; D003624:Darkness; D005453:Fluorescence; D010788:Photosynthesis / Q000187:drug effects*; D045332:Photosystem II Protein Complex / Q000378:metabolism; D010860:Pigments, Biological / Q000378:metabolism; D064201:Trichomes / Q000033:anatomy & histology / Q000187:drug effects
chemical_list: D045332:Photosystem II Protein Complex; D010860:Pigments, Biological; D002245:Carbon Dioxide; D002244:Carbon
keywords: CCM; CO(2); Cylindrospermopsis raciborskii; Energy; PSII; Photosynthesis