title: The slow S to M rise of chlorophyll a fluorescence reflects transition from state 2 to state 1 in the green alga Chlamydomonas reinhardtii.
abstract: The green alga Chlamydomonas (C.) reinhardtii is a model organism for photosynthesis research. State transitions regulate redistribution of excitation energy between photosystem I (PS I) and photosystem II (PS II) to provide balanced photosynthesis. Chlorophyll (Chl) a fluorescence induction (the so-called OJIPSMT transient) is a signature of several photosynthetic reactions. Here, we show that the slow (seconds to minutes) S to M fluorescence rise is reduced or absent in the stt7 mutant (which is locked in state 1) in C. reinhardtii. This suggests that the SM rise in wild type C. reinhardtii may be due to state 2 (low fluorescence state; larger antenna in PS I) to state 1 (high fluorescence state; larger antenna in PS II) transition, and thus, it can be used as an efficient and quick method to monitor state transitions in algae, as has already been shown in cyanobacteria (Papageorgiou et al. 1999, 2007; Kaňa et al. 2012). We also discuss our results on the effects of (1) 3-(3,4-dichlorophenyl)-1,4-dimethyl urea, an inhibitor of electron transport; (2) n-propyl gallate, an inhibitor of alternative oxidase (AOX) in mitochondria and of plastid terminal oxidase in chloroplasts; (3) salicylhydroxamic acid, an inhibitor of AOX in mitochondria; and (4) carbonyl cyanide p-trifluoromethoxyphenylhydrazone, an uncoupler of phosphorylation, which dissipates proton gradient across membranes. Based on the data presented in this paper, we conclude that the slow PSMT fluorescence transient in C. reinhardtii is due to the superimposition of, at least, two phenomena: qE dependent non-photochemical quenching of the excited state of Chl, and state transitions.
authors: Department of Plant Sciences, School of Life Sciences, University of Hyderabad, Hyderabad, 500 046, India.
authors: Sireesha
authors: S
authors: Kodru
authors: Tirupathi
authors: T
authors: Malavath
authors: Elsinraju
authors: E
authors: Devadasu
authors: Sreedhar
authors: S
authors: Nellaepalli
authors: Alexandrina
authors: A
authors: Stirbet
authors: Rajagopal
authors: R
authors: Subramanyam
authors: Govindjee
mesh_terms: D016825:Chlamydomonas reinhardtii / Q000378:metabolism*; D002734:Chlorophyll / Q000031:analogs & derivatives / Q000378:metabolism; D000077194:Chlorophyll A; D002736:Chloroplasts / Q000201:enzymology; D004579:Electron Transport; D005453:Fluorescence; D008027:Light; D045342:Light-Harvesting Protein Complexes / Q000378:metabolism*; D008928:Mitochondria / Q000201:enzymology; D024101:Mitochondrial Proteins / Q000378:metabolism; D010088:Oxidoreductases / Q000378:metabolism; D010788:Photosynthesis; D045331:Photosystem I Protein Complex / Q000378:metabolism*; D045332:Photosystem II Protein Complex / Q000378:metabolism*; D010940:Plant Proteins / Q000378:metabolism; D000099188:Alternative Oxidase
chemical_list: D002734:Chlorophyll; D000077194:Chlorophyll A; D045342:Light-Harvesting Protein Complexes; D024101:Mitochondrial Proteins; D010088:Oxidoreductases; D045331:Photosystem I Protein Complex; D045332:Photosystem II Protein Complex; D010940:Plant Proteins; D000099188:Alternative Oxidase; C085815:chlorophyll a'