Cyclic electron flow around photosystem I is enhanced at low pH

Area of Science:

• Plant Physiology
• Photosynthesis Research
• Biochemistry

Background:

• Photosystem II (PS II) fluorescence decreases while Photosystem I (PSI) fluorescence increases at low pH (5.5).
• Understanding the mechanisms behind these fluorescence changes is crucial for photosynthesis research.

Purpose of the Study:

• To investigate the reasons for observed changes in PS II and PS I fluorescence at different pH levels.
• To elucidate the role of pH in regulating photosynthetic electron transport and protecting PSI.

Main Methods:

• Spinach leaf discs were treated with buffers at pH 7.5, 6.5, and 5.5.
• Measurements included photochemical quantum yield of PS II (Y(II)) and PS I (Y(I)).
• Analysis of trans-thylakoid pH gradient, non-photochemical quenching, and electron transport rate.

Main Results:

• A decrease in Y(II) and an increase in Y(I) were observed at low pH.
• Enhanced protection against PSI acceptor side over-reduction was noted at pH 5.5.
• Low pH induced a rapid build-up of the trans-thylakoid pH gradient, increased non-photochemical quenching, and decreased PS II electron transport rate.

Conclusions:

• A strong stimulation of cyclic electron flow around PSI at pH 5.5 was suggested.
• This cyclic flow provides protection against PSI acceptor side over-reduction.
• The findings highlight the importance of pH regulation in maintaining photosynthetic efficiency.