Evidence for reversible light-dependent transitions in the photosynthetic pigments of diatoms

• Published in: RSC advances Vol. 12; no. 49; pp. 31555 - 31563
• Main Authors: Tselios, Charalampos, Varotsis, Constantinos
• Format: Journal Article
• Language: English
• Published: Cambridge Royal Society of Chemistry 03-11-2022; The Royal Society of Chemistry
• Subjects: Blue shift; Chemistry; Chlorophyll; Energy harvesting; Energy transfer; Light; Luminous intensity; Photosynthesis; Pigments; Plankton; Porphyrins; Raman spectra; Room temperature; Temperature dependence
• ISSN: 2046-2069; 2046-2069
• DOI: 10.1039/d2ra05284a

Marine diatoms contribute to oxygenic photosynthesis and carbon fixation and handle large changes under variable light intensity on a regular basis. The unique light-harvesting apparatus of diatoms are the fucoxanthin-chlorophyll
a
/
c
-binding proteins (FCPs). Here, we show the enhancement of chlorophyll
a
/
c
(Chl
a
/
c
), fucoxanthin (Fx), and diadinoxanthin (Dd) marker bands in the Raman spectra of the centric diatom
T. pseudonana
, which allows distinction of the pigment content in the cells grown under low- (LL) and high-light (HL) intensity at room temperature. Reversible LL-HL dependent conformations of Chl
c
, characteristic of two conformations of the porphyrin macrocycle, and the presence of five- and six-coordinated Chl
a
/
c
with weak axial ligands are observed in the Raman data. Under HL the energy transfer from Chl
c
to Chl
a
is reduced and that from the red-shifted Fxs is minimal. Therefore, Chl
c
and the blue-shifted Fxs are the only contributors to the energy transfer pathways under HL and the blue- to red-shifted Fxs energy transfer pathway characteristic of the LL is inactive. The results indicate that
T. pseudonana
can redirect its function from light harvesting to energy-quenching state, and reversibly to light-harvesting upon subsequent illumination to LL by reproducing the red-shifted Fxs and decrease the number of Dds. The LL to HL reversible transitions are accompanied by structural modifications of Chl
a
/
c
and the lack of the red-shifted Fxs.
A reversible light-intensity behavior of Dds and Fxs composition in the cells of
T. pseudonana
. The observed LL to HL reversible transitions are accompanied by structural modifications of Chls
a
/
c
and the lack of the red-shifted Fxs.