A Kinetic Model of Non-Photochemical Quenching in Cyanobacteria and Implications for Interpretation of Solar-Induced Fluorescence Signals

Maxim Gorbunov, Rutgers University, gorbunov@marine.rutgers.edu (Presenter)
Fedor Kuzminov, Rutgers University, fedor.kouzminov@gmail.com
Victor Fadeev, Moscow State University, victor_fadeev@mail.ru
John Dongun Kim, Rutgers University, 0johnkim@gmail.com
Paul Falkowski, Rutgers University, falko@marine.rutgers.edu

High light poses a threat to oxygenic photosynthetic organisms. Similar to plants and eukaryotic algae, cyanobacteria evolved a photoprotective mechanism, non-photochemical quenching (NPQ), which dissipates excess absorbed energy as heat. Cyanobacteria lack both pH-dependent quenching or the xanthophyll cycle. However, an orange carotenoid protein (OCP) has been implicated as a blue-green light sensor that can induce NPQ in cyanobacteria. Discovered in-vitro, this reaction involves a light-induced transformation of the OCP from its dark, orange form (OCPo) to a red, active form, however, the molecular and biophysical mechanisms of NPQ in vivo remain largely unknown. Here we show that the formation of the quenching state in vivo is a multistep process that involves both photoinduced and dark reactions. Our kinetic analysis of the NPQ process reveals that the light induced conversion of OCPo to a quenching state (OCPq) proceeds via an intermediate, non-quenching state (OCPi), and this reaction sequence can be described by a three-state kinetic model. The conversion of OCPo to OCPi is a photoinduced process with the effective absorption cross section of 4.5 × 10-3 A2 at 470 nm. The transition from OCPi to OCPq is a dark reaction, with the first order rate constant of ~ 0.1 s-1 at 25 oC and the Arrhenius activation energy of 21 kcal/mol. These kinetic and thermodynamic characteristics suggest that the rate of formation of the quenched centers may be limited by cis-trans proline isomerization of Gln224-Pro225 or Pro225-Pro226 in the OCP. The quantum yield of formation of the quenched state is 0.1%. Kinetic fluorescence analysis revealed that the quenching of Fm fluorescence is accompanied by a proportional decrease in the functional absorption cross-section of Photosystem II, suggesting that formation of the quenched centers reduces the flux of absorbed energy from phycobilisomes to the reaction centers by ~50%. We further compare the molecular mechanisms of NPQ in cyanobacteria and eukaryotic algae, together with the implications for variability in satellite-based solar-induced fluorescence yields.

Presentation Type:  Poster

Session:  Coupled Processes at Land-Atmosphere-Ocean Interfaces   (Mon 4:00 PM)

Associated Project(s): 

• Gorbunov, Maxim: The application of lifetime analyses in the upper ocean to the interpretation of satellite-based solar induced fluorescence signals ...details

Poster Location ID: 29