Photosystem I Is Indispensable for Photoautotrophic Growth, CO2 Fixation, and H2 Photoproduction inChlamydomonas reinhardtii

We find no instance of a strain that can perform photosynthesis in the absence of photosystem I

Kevin Redding


Scholarcy highlights

  • The proposal that two different light reactions are involved in oxygenic photosynthesis arose from studies of an “enhancement effect” that was observed when two beams of different wavelengths were used to illuminate algae
  • Certain Chlamydomonas reinhardtii mutants deficient in photosystem I due to defects in psaA mRNA maturation have been reported to be capable of CO2 fixation, H2 photoevolution, and photoautotrophic growth (Greenbaum, E., Lee, J
  • Other explanations have been proffered for the enhancement effect and photosystem cooperativity, the Z-scheme is strongly supported by experimental data and is currently considered as the “central dogma” of oxygenic photosynthesis
  • CO2 fixation in the photosystem I-deficient strains initially appeared to be limited to anaerobic conditions, photoautotrophic growth was later reported in the presence of O2
  • The rise in fluorescence, which is correlated with reduced QA in photosystem II, is due to the reduction of the plastoquinone pool, while the subsequent drop has been interpreted as originating from oxidation of the plastoquinone pool due to the combined action of PS I and cytochrome b6f
  • We estimated that these polypeptides were present at roughly 10% of the WT amount when normalized to total membrane protein
  • We find that the in vivo capabilities of photoautotrophic growth, CO2 fixation, and H2 evolution require the presence of active PS I
  • Our results indicate that one must be very careful in the choice of mutant to study; mutants defective in expression can be suppressed and small deletions in genes can be repaired, but large deletions of entire open reading frames encoding key structural components cannot revert or result in leaky phenotypes

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