Abstract
Throughout the history of oxygen evolution, two types of photosystem reaction centres (PSI and PSII) have worked in a coordinated manner. The oxygen evolving centre is an integral part of PSII, and extracts an electron from water. PSI accepts the electron, and accumulates reducing power. Traditionally, PSI and PSII are thought to be spatially dispersed. Here, we show that about half of PSIIs are physically connected to PSIs in Arabidopsis thaliana. In the PSI-PSII complex, excitation energy is transferred efficiently between the two closely interacting reaction centres. PSII diverts excitation energy to PSI when PSII becomes closed-state in the PSI-PSII complex. The formation of PSI-PSII complexes is regulated by light conditions. Quenching of excess energy by PSI might be one of the physiological functions of PSI-PSII complexes.
Highlights
Throughout the history of oxygen evolution, two types of photosystem reaction centres (PSI and PSII) have worked in a coordinated manner
We combined large-pore clear-native polyacrylamide gel electrophoresis (PAGE) and time-resolved spectroscopy to examine whether PSI and PSII interact with each other in Arabidopsis thaliana
We examined whether PSI–PSII complexes existed in A. thaliana by delayed fluorescence analysis
Summary
Throughout the history of oxygen evolution, two types of photosystem reaction centres (PSI and PSII) have worked in a coordinated manner. In PSI–PSII complexes isolated by lpCN-PAGE, excitation energy is transferred efficiently between the two closely interacting reaction centres. Delayed fluorescence should appear in the PSI wavelength region at À 196 °C if PSI–PSII complexes exist[12].
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