Phycobilisome diffusion is required for light-state transitions in cyanobacteria

Area of Science:

• Photosynthesis research
• Cellular biophysics
• Algal physiology

Background:

• Phycobilisomes are key accessory light-harvesting complexes in cyanobacteria and red algae.
• In vivo studies show phycobilisomes rapidly diffuse on thylakoid membranes, unlike immobile PSII core complexes, indicating transient associations.
• This transient interaction suggests phycobilisomes may detach from reaction centers.

Purpose of the Study:

• To investigate the effect of osmotic strength on phycobilisome mobility in cyanobacteria.
• To determine if phycobilisome diffusion is linked to physiological adaptation mechanisms like state transitions.
• To elucidate the role of phycobilisome mobility in light-harvesting regulation.

Main Methods:

• Utilized fluorescence recovery after photobleaching (FRAP) in vivo.
• Applied high osmotic strength buffers to Synechococcus sp. PCC7942 cells.
• Measured changes in phycobilisome diffusion coefficients under varying osmotic conditions.
• Assessed the impact on state transitions, a mechanism regulating light energy distribution.

Main Results:

• High osmotic strength buffers significantly decreased phycobilisome diffusion coefficients in Synechococcus sp. PCC7942.
• This reduction in mobility suggests a less transient interaction between phycobilisomes and reaction centers.
• High osmotic strength buffers inhibited state transitions at concentrations similar to those affecting diffusion.

Conclusions:

• Phycobilisome diffusion is necessary for state transitions, a crucial light-adaptation mechanism.
• The mobility of phycobilisomes is likely essential for flexible and efficient light harvesting in cyanobacteria.
• Osmotic stress can alter phycobilisome-thylakoid interactions, impacting energy distribution.