Spectrally decomposed dark-to-light transitions in Synechocystis sp. PCC 6803

Alonso M. Acuña, Pascal van Alphen, Filipe Branco Dos Santos, Rienk van Grondelle, Klaas J. Hellingwerf, Ivo H.M. van Stokkum*

*Corresponding author for this work

Research output: Contribution to JournalArticleAcademicpeer-review


Photosynthetic activity and respiration share the thylakoid membrane in cyanobacteria. We present a series of spectrally resolved fluorescence experiments where whole cells of the cyanobacterium Synechocystis sp. PCC 6803 and mutants thereof underwent a dark-to-light transition after different dark-adaptation (DA) periods. Two mutants were used: (i) a PSI-lacking mutant (ΔPSI) and (ii) M55, a mutant without NAD(P)H dehydrogenase type-1 (NDH-1). For comparison, measurements of the wild-type were also carried out. We recorded spectrally resolved fluorescence traces over several minutes with 100 ms time resolution. The excitation light was at 590 nm so as to specifically excite the phycobilisomes. In ΔPSI, DA time has no influence, and in dichlorophenyl-dimethylurea (DCMU)-treated samples we identify three main fluorescent components: PB–PSII complexes with closed (saturated) RCs, a quenched or open PB–PSII complex, and a PB–PSII ‘not fully closed.’ For the PSI-containing organisms without DCMU, we conclude that mainly three species contribute to the signal: a PB–PSII–PSI megacomplex with closed PSII RCs and (i) slow PB → PSI energy transfer, or (ii) fast PB → PSI energy transfer and (iii) complexes with open (photochemically quenched) PSII RCs. Furthermore, their time profiles reveal an adaptive response that we identify as a state transition. Our results suggest that deceleration of the PB → PSI energy transfer rate is the molecular mechanism underlying a state 2 to state 1 transition.

Original languageEnglish
Pages (from-to)307–320
Number of pages14
JournalPhotosynthesis Research
Issue number2
Early online date29 Mar 2018
Publication statusPublished - Aug 2018


  • Cyanobacteria
  • Cyclic electron flow
  • Plastoquinone pool
  • Singular value decomposition
  • Spectrally resolved fluorometry
  • Time-resolved spectroscopy


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