REGULAR PAPER Effect of dichromate on photosystem II activity in xanthophyll- deficient mutants of Chlamydomonas reinhardtii Nadia Ait Ali Æ Philippe Juneau Æ Olivier Didur Æ Franc ¸ois Perreault Æ Radovan Popovic Received: 6 March 2007 / Accepted: 12 July 2007 / Published online: 12 September 2007 Ó Springer Science+Business Media B.V. 2007 Abstract The photosystem II activity and energy dissi- pation was investigated when algal Chlamydomonas reinhardtii genotypes were exposed to dichromate toxicity effect. The exposure during 24 h to dichromate effect of two C. reinhardtii mutants having non-functional xantho- phylls cycle, as npq1 zeaxanthin deficient and npq2 zeaxanthin accumulating, induced inhibition of PSII elec- tron transport. After dichromate-induced toxicity, PSII functions of C. reinhardtii mutants were investigated under different light intensities. To determine dichromate toxicity and light intensity effect on PSII functional properties we investigated the change of energy dissipation via PSII electron transport, non-photochemical regulated and non- regulated energy dissipation according to Kramer et al. (Photosynth Res 79:209–218, 2004). We showed the dependency between dichromate toxicity and light-induced photoinhibition in algae deficient in xanthophyll cycle. When algal mutants missing xanthophylls cycle were exposed to dichromate toxicity and to high light intensity energy dissipation via non-regulated mechanism takes the most important pathway reaching the value of 80%. Therefore, the mutants npq1 and npq2 having non-func- tional xanthophylls cycle were more sensitive to dichro- mate toxic effects. Keywords Photosystem II energy dissipation Á Xanthophyll cycle Á Zeaxanthin Á Dichromate Á Chlamydomonas reinhardtii Á MAXI-IMAGING-PAM fluorometry Abbreviations D1 A core protein of the photosystem II reaction center DCPIP 2,6-dichlorophenol indophenol DPC Diphenyl-carbazide F O and F O 0 Fluorescence yields when all reaction centers of PSII are oxidized under dark and light adapted state, respectively F M and F M 0 Maximal fluorescence yields in dark and light adapted state, respectively F Fluorescence yield at any time of induction by an actinic radiation LHC Light harvesting complexes NPQ Fluorescence non-photochemical quenching PSII Photosystem II qL Fraction of open PSII reaction center participating in electron transport qP Fluorescence photochemical quenching Q A and Q B PSII primary and secondary electron acceptors, respectively ROS Reactive oxygen species Y(II) Effective quantum yield of PSII photochemistry Y(NPQ) Quantum yield of regulated energy dissipation of PSII Y(NO) Quantum yield of non-regulated energy dissipation of PSII N. Ait Ali Á O. Didur Á F. Perreault Á R. Popovic (&) Department of Chemistry, Environmental Toxicology Research Center, TOXEN, University of Quebec in Montreal, 2101, Jeanne-Mance, Montreal, QC, Canada H2X 2J6 e-mail: popovic.radovan@uqam.ca P. Juneau Department of Biological Sciences – TOXEN, Canadian Research Chair on Ecotoxicology of Aquatic Microorganisms, University of Quebec in Montreal, C.P. 8888, Succ. Centre-ville, Montreal, QC, Canada H3C 3P8 123 Photosynth Res (2008) 95:45–53 DOI 10.1007/s11120-007-9227-4