Photosystem II heterogeneity: the acceptor side.

Area of Science:

• Plant Biology
• Photosynthesis Research
• Biophysics

Background:

• Oxygenic photosynthesis relies on Photosystem I and II (PSI and PSII) for electron transfer from H2O to NADP+.
• Each photosystem comprises light-harvesting antenna (L-HA) systems, reaction center (RC) complexes, and electron/proton transport components.
• Heterogeneity in the electron acceptor side of PSII, including L-HA systems and reaction centers, is well-established.

Purpose of the Study:

• To review heterogeneity in the electron acceptor side of Photosystem II (PSII).
• To discuss the implications of PSII heterogeneity on the ratio of PSII to PSI reaction centers (RC-II/RC-I).
• To present recent findings on the relationship between active and inactive RC-II using specific quinones and fluorescence measurements.

Main Methods:

• Mini-review of existing literature on PSII heterogeneity.
• Analysis of electron acceptor components including QA, QB, and other co-factors.
• Utilizing quinones (DMQ, DCBQ) and fluorescence transient measurements.
• Investigating heated spinach and soybean thylakoids.

Main Results:

• Identified heterogeneity in PSII's L-HA system (PSIIα, PSIIβ) and reaction centers (Q1, Q2).
• Characterized diverse forms of QB and electron acceptors like QA (QL, QH), iron, U, and Q-318.
• Demonstrated that inactive RC-II can be monitored via the OID phase of fluorescence transients.
• Showed that heating converts active RC-II into inactive forms.

Conclusions:

• The electron acceptor side of PSII displays significant heterogeneity, impacting electron flow.
• Active and inactive RC-II populations are distinguishable and interconvertible.
• Fluorescence transient analysis, particularly the OID phase, is a valuable tool for studying RC-II states and their environmental responses.