Mechanism of adiabatic primary electron transfer in photosystem I: Femtosecond spectroscopy upon excitation of reaction center in the far-red edge of the QY band

Abstract

The ultrafast primary charge separation in Photosystem I (PS I) excited by femtosecond pulses centered at 720 and 760nm was studied by pump-to-probe laser spectroscopy. The absorbance in the red edge of PS I absorption spectrum has an unusual exponential dependence on wavelength. The cutoff of short wavelength components of 760nm pulse allows direct excitation of reaction center chlorophyll molecules without involvement of light-harvesting antenna. The transient spectrum manifests the features of the primary ion-radical pair PA at time delay <180fs, followed by formation of the secondary pair PA with a characteristic time of 26ps. The obtained data are rationalized in the framework of adiabatic three-state model that includes the chlorophyll dimer P and two symmetrically arranged nearest chlorophyll molecules of A. The arrangement of chlorophylls results in strong electronic coupling between P and A. Excitation in the maximum of P absorption generates electronic states with the highest contribution from P*, whereas excitation in the far-red edge predominantly generates charge transfer state PA in both branches of redox-cofactors. The three-level model accounts for a flat-bottomed potential surface of the excited state and adiabatic character of electron transfer between P and A, providing a microscopic explanation of the ultrafast formation of PA and exponential decline of PS I absorption.

NaCl improves reproduction by enhancing starch accumulation in the ovules of the euhalophyte Suaeda salsa

“…We identi ed 28 photosynthesis-related DEGs between NaCl-treated and control plants (Additional le 5: Figure S5), leading to differences in oxygen releasing e ciency in petals between the two groups of S. salsa (Additional le 4: Figure S4). PSI and PSII are the main components of the photosynthetic apparatus in plants [56,57], including the proximal antenna of PSII (cp43) [79] and the PSI subunits PsaF and PsaN [58]. In the present study, DEGs related to photosynthesis, such as genes encoding PsbP and PsbR, were downregulated in NaCl-treated S. salsa owers (Fig.…”

“…This complex is responsible for light harvesting and electron transport during photosynthesis immediately after water oxidation [56]. PSI, a chlorophyll-protein complex, catalyzes the transfer of electrons from plastocyanin/cytochrome c6 to ferredoxin/flavodoxin, a process driven by light [57]. The PSI subunits PsaF and PsaN interact with ferredoxin or plastocyanin [58].…”

Comparisons of Electron Transfer Reactions in a Cyanobacterial Tetrameric and Trimeric Photosystem I Complexes

“…New data in isolated PSI complexes from cyanobacteria Synechocystis sp. PCC 6803 excited by femtosecond pulse at the far‐red edge of Q Y absorption band were recently obtained . In this work, the authors were able to show that excitation in the maximum of P 700 absorption generates electronic states with the highest contribution from P 700 *, whereas excitation in the far‐red edge predominantly generates charge transfer state P 700 + A 0 − in both branches of redox cofactors.…”

“…However, Refs. and have shown that after preferential excitation of P 700 and A 0 , formation of primary radical pair P 700 + A 0 − occurs, within 100 fs, and the formation of P 700 + A 1 − has a characteristic time of ~25 ps.…”

“…However, Refs. (16) and (22) have shown that after preferential excitation of P 700 and A 0 , formation of primary radical pair P 700 + A 0 À occurs, within 100 fs, and the formation of P 700 + A 1 À has a characteristic time of~25 ps. Subsequent electron transfer reactions from A 1A and A 1B to F X take place with characteristic times of~200 and~20 ns, respectively (14,(23)(24)(25).…”