Effect of dichromate on photosystem II activity in xanthophyll-deficient mutants of Chlamydomonas reinhardtii.

The photosystem II activity and energy dissipation 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 xanthophylls cycle, as npq1 zeaxanthin deficient and npq2 zeaxanthin accumulating, induced inhibition of PSII electron 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-functional xanthophylls cycle were more sensitive to dichromate toxic effects.