title: Effect of cadmium on photosystem II activity in Chlamydomonas reinhardtii: alteration of O-J-I-P fluorescence transients indicating the change of apparent activation energies within photosystem II.
abstract: In this study, we evaluated how cadmium inhibitory effect on photosystem II and I electron transport may affect light energy conversion into electron transport by photosystem II. To induce cadmium effect on the photosynthetic apparatus, we exposed Chlamydomonas reinhardtii 24 h to 0-4.62 μM Cd(2+). By evaluating the half time of fluorescence transients O-J-I-P at different temperatures (20-30°C), we were able to determine the photosystem II apparent activation energies for different reduction steps of photosystem II, indicated by the O-J-I-P fluorescence transients. The decrease of the apparent activation energies for PSII electron transport was found to be strongly related to the cadmium-induced inhibition of photosynthetic electron transport. We found a strong correlation between the photosystem II apparent activation energies and photosystem II oxygen evolution rate and photosystem I activity. Different levels of cadmium inhibition at photosystem II water-splitting system and photosystem I activity showed that photosystem II apparent activation energies are strongly dependent to photosystem II donor and acceptor sides. Therefore, the oxido-reduction state of whole photosystem II and I electron transport chain affects the conversion of light energy from antenna complex to photosystem II electron transport.
authors.affiliation: Department of Chemistry, Université du Québec à Montréal, Case Postale 8888, Succursale Centre-Ville, Montréal, QC H3C 3P8, Canada.
authors.forename: François
authors.initials: F
authors.lastname: Perreault
authors.forename: Jérôme
authors.initials: J
authors.lastname: Dionne
authors.forename: Olivier
authors.initials: O
authors.lastname: Didur
authors.forename: Philippe
authors.initials: P
authors.lastname: Juneau
authors.forename: Radovan
authors.initials: R
authors.lastname: Popovic
mesh_terms: D002104:Cadmium / Q000494:pharmacology*; D016825:Chlamydomonas reinhardtii / Q000187:drug effects* / Q000502:physiology; D004579:Electron Transport / Q000187:drug effects; D005453:Fluorescence; D007700:Kinetics; D010788:Photosynthesis / Q000187:drug effects / Q000502:physiology; D045332:Photosystem II Protein Complex / Q000187:drug effects* / Q000378:metabolism; D013696:Temperature
chemical_list: D045332:Photosystem II Protein Complex; D002104:Cadmium