Excitation energy transfer dynamics in a red-shifted chlorophyll-a light harvesting complex from eustigmatophytes

David Bínaa,b, Milan Durchana,b, Valentyna Kuznetsovab, Tomáš Polívkaa,b, Radek Litvína,b
aInstitute of Plant Molecular Biology, Biology Centre CAS, Branišovská 31, 370 05 České Budějovice, Czech Republic; bFaculty of Science, University of South Bohemia Branišovská 1760, 370 05 České Budějovice, Czech Republic

Organisms inhabiting bottom layers of a stratified phototrophic community face the effect of shading: incident radiation depleted by wavelengths absorbed by chlorophyll-a and carotenoids, leading to relative enhancement of the far red part of the spectrum. It is well known that this niche can be occupied by Cyanobacteria synthesizing red-shifted chlorophylls such as Chl d or Chl f [1] but only recently it has become apparent that the spectral window in the region 680-720 nm is utilized by a diverse group of algae using specialized chlorophyll-a based antenna complexes.

Here we present an ultrafast transient absorption study of the excitation energy flow in a red-shifted Chl-a pigment-protein complex which forms the main component of the light-harvesting apparatus of the alga Trachydiscus minutus (Eustigmatophyceae). Excitation energy transfer was studied following excitation into carotenoid and chlorophyll-a absorption bands. Experiments were performed at 77 K. At least two spectral pools of carotenoids were identified, transferring excitation to Chl‑a acceptor states at ~675 nm and ~700 nm. The terminal Chl-a state lies at ~705 nm.  


[1] Y. Li and M. Chen, Functional Plant Biol. 2015, 42, 493.