Plants acclimate to Photosystem I photoinhibition by readjusting the photosynthetic machinery

Photosynthetic light reactions require strict regulation under dynamic environmental conditions. Still, depending on environmental constraints, photoinhibition of Photosystem (PSII) or PSI occurs frequently. Repair of photodamaged PSI, in sharp contrast to that of PSII, is extremely slow and leads to a functional imbalance between the photosystems. Slow PSI recovery prompted us to take advantage of the PSI-specific photoinhibition treatment and investigate whether the imbalance between functional PSII and PSI leads to acclimation of photosynthesis to PSI-limited conditions, either by short-term or long-term acclimation mechanisms as tested immediately after the photoinhibition treatment or after 24 h recovery in growth conditions, respectively. Short-term acclimation mechanisms were induced directly upon inhibition, including thylakoid protein phosphorylation that redirects excitation energy to PSI as well as changes in the feedback regulation of photosynthesis, which relaxed photosynthetic control and excitation energy quenching. Longer-term acclimation comprised reprogramming of the stromal redox system and an increase in ATP synthase and Cytochrome b(6)f abundance. Acclimation to PSI-limited conditions restored the CO2 assimilation capacity of plants without major PSI repair. Response to PSI inhibition demonstrates that plants efficiently acclimate to changes occurring in the photosynthetic apparatus, which is likely a crucial component in plant acclimation to adverse environmental conditions.

Automated summary

Photosynthetic light reactions require strict regulation under dynamic environmental conditions. Depending on environmental constraints, photoinhibition of either Photosystem II (PSII) or Photosystem I (PSI) occurs frequently. Repair of photodamaged PSI is very slow compared to that of PSII, leading to a functional imbalance between the two photosystems. In this study, we investigated the acclimation of photosynthesis to PSI-limited conditions, both in the short-term and long-term, after PSI-specific photoinhibition treatment. We found that short-term acclimation mechanisms were induced immediately after inhibition, while longer-term acclimation involved changes in the stromal redox system and increased abundance of ATP synthase and Cytochrome b6f. Acclimation to PSI-limited conditions restored the CO2 assimilation capacity of plants without major PSI repair. These findings demonstrate that plants efficiently acclimate to changes in the photosynthetic apparatus, which is crucial for their adaptation to adverse environmental conditions.