Phycobilisome composition and possible relationship to reaction centers

Area of Science:

• Photosynthesis research
• Cyanobacterial physiology
• Pigment mutant analysis

Background:

• Anacystis nidulans wild type and a pigment mutant 85Y were studied.
• Mutant 85Y exhibits enhanced growth in far-red light (>650 nm).
• Phycobiliprotein composition and phycobilisome structure were investigated.

Purpose of the Study:

• To characterize the photosynthetic apparatus in Anacystis nidulans wild type and mutant 85Y.
• To understand the structural and compositional differences in phycobilisomes.
• To investigate the adaptation of the photosynthetic apparatus under far-red light conditions.

Main Methods:

• Comparative analysis of C-phycocyanin and allophycocyanin ratios.
• Measurement of phycobilisome size and fluorescence emission/excitation spectra.
• Determination of thylakoid area and chlorophyll content per cell.
• Calculation of phycobilisome number per cell and per unit thylakoid area.

Main Results:

• Mutant 85Y showed a lower C-phycocyanin to allophycocyanin ratio and smaller phycobilisomes compared to wild type.
• Phycobilisomes in mutant 85Y appeared to consist mainly of the allophycocyanin core.
• Thylakoid area and chlorophyll content per cell were reduced in far-red light, especially in the mutant.
• Phycobilisomes per unit thylakoid area were significantly higher in mutant 85Y.

Conclusions:

• Phycobilisomes are suggested to be linked with reaction centers.
• The photo-system II complement, including phycobilisomes, is maintained in far-red light.
• Mutant 85Y demonstrates an effective adaptation strategy for far-red light growth through altered phycobilisome organization.