title: The slow phase of chlorophyll a fluorescence induction in silico: Origin of the S-M fluorescence rise.
abstract: In higher plants, algae, and cyanobacteria, chlorophyll (Chl) a fluorescence induction (ChlFI) has a fast (under a second) increasing OJIP phase and a slow (few minutes) PS(M)T phase, where O is for origin, the minimum fluorescence, J and I for intermediate levels, P for peak, S for a semi-steady state, M for a maximum (which is sometimes missing), and T for the terminal steady-state level. We have used a photosynthesis model of Ebenhöh et al. (Philos Trans R Soc B, 2014, doi: 10.1098/rstb.2013.0223 ) in an attempt to simulate the slow PS(M)T phase and to determine the origin of the S-M rise in Chlamydomonas (C.) reinhardtii cells. Our experiments in silico show that a slow fluorescence S-M rise (as that observed, e.g., by Kodru et al. (Photosynth Res 125:219-231, 2015) can be simulated only if the photosynthetic samples are initially in a so-called "state 2," when the absorption cross section (CS) of Photosystem II (PSII) is lower than that of PSI, and Chl a fluorescence is low (see, e.g., a review by Papageorgiou and Govindjee (J Photochem Photobiol B 104:258-270, 2011). In this case, simulations show that illumination induces a state 2 (s2) to state 1 (s1) transition (qT21), and a slow S-M rise in the simulated ChlFI curve, since the fluorescence yield is known to be higher in s1, when CS of PSII is larger than that of PSI. Additionally, we have analyzed how light intensity and several photosynthetic processes influence the degree of this qT21, and thus the relative amplitude of the simulated S-M phase. A refinement of the photosynthesis model is, however, necessary in order to obtain a better fit of the simulation data with the measured ChlFI curves.
authors.affiliation: , 204 Anne Burras Ln, Newport News, VA, 23606, USA.
authors.forename: Alexandrina
authors.initials: A
authors.lastname: Stirbet
authors.affiliation: Department of Biochemistry, Department of Plant Biology, and Center of Biophysics & Quantitative Biology, University of Illinois at Urbana-Champaign, Urbana, IL, 61801-3707, USA. gov@illinois.edu.
authors.lastname: Govindjee
mesh_terms: D016825:Chlamydomonas reinhardtii / Q000378:metabolism; D002734:Chlorophyll / Q000737:chemistry*; D000077194:Chlorophyll A; D003198:Computer Simulation; D005453:Fluorescence; D010788:Photosynthesis; D045332:Photosystem II Protein Complex / Q000378:metabolism
chemical_list: D045332:Photosystem II Protein Complex; D002734:Chlorophyll; D000077194:Chlorophyll A
keywords: Anoxia; Chlamydomonas reinhardtii; Mathematical simulation; Nonphotochemical quenching; Photosynthesis model; Slow Chl a fluorescence induction; State transitions