Energy transfer from phycobilisomes to photosystem I at 77 K

Ivo H M van Stokkum; Parveen Akhtar; Avratanu Biswas; Petar H Lambrev

doi:10.3389/fpls.2023.1293813

Energy transfer from phycobilisomes to photosystem I at 77 K

Front Plant Sci. 2023 Nov 22:14:1293813. doi: 10.3389/fpls.2023.1293813. eCollection 2023.

Authors

Ivo H M van Stokkum^#¹, Parveen Akhtar^#², Avratanu Biswas^{1

2

3}, Petar H Lambrev²

Affiliations

¹ Department of Physics and Astronomy and LaserLaB, Faculty of Science, Vrije Universiteit Amsterdam, Amsterdam, Netherlands.
² Institute of Plant Biology, HUN-REN Biological Research Centre, Szeged, Hungary.
³ Doctoral School of Biology, University of Szeged, Szeged, Hungary.

^# Contributed equally.

Abstract

Phycobilisomes serve as a light-harvesting antenna of both photosystem I (PSI) and II (PSII) in cyanobacteria, yet direct energy transfer from phycobilisomes to PSI is not well documented. Here we recorded picosecond time-resolved fluorescence at wavelengths of 605-760 nm in isolated photosystem I (PSI), phycobilisomes and intact cells of a PSII-deficient mutant of Synechocystis sp. PCC 6803 at 77 K to study excitation energy transfer and trapping. By means of a simultaneous target analysis of the kinetics of isolated complexes and whole cells, the pathways and dynamics of energy transfer in vitro and in vivo were established. We establish that the timescale of the slowest equilibration between different terminal emitters in the phycobilisome is ≈800 ps. It was estimated that the terminal emitter in about 40% of the phycobilisomes transfers its energy with a rate constant of 42 ns^-1 to PSI. This energy transfer rate is higher than the rates of equilibration within the phycobilisome - between the rods and the core or between the core cylinders - and is evidence for the existence of specific phycobilisome-PSI interactions. The rest of the phycobilisomes remain unconnected or slowly transferring energy to PSI.

Keywords: Synechocystis sp. PCC 6803; cyanobacteria; photosynthesis; photosystems; thylakoid membranes; time-resolved fluorescence.

Grants and funding

The author(s) declare financial support was received for the research, authorship, and/or publication of this article. The work was supported by grants from the National Research, Development and Innovation Fund (NKFI FK-139067 to PA and ANN-144012 and 2018-1.2.1-NKP-2018-00009 to PL) and the Hungarian Research Network (SA-76/2021 to PA).