No abstract

The role of melatonin (MLT) in micro-and macroalgae is the subject of continuous discussion. In eukaryotic unicellular organisms, the physiological role of MLT seems to differ from those of higher plants and mammals. Experimental data on the role of MLT in algae suggest that it acts mainly as an antioxidant. In the present study, the physiological role of MLT in phototrophic organisms was studied by measuring its effects on periodically controlled processes (cell division and HSP70B expression) as well as mechanisms involved in oxidative stress protection (carotenoids, FeSOD and MnSOD expression). The presence of MLT in Chlamydomonas reinhardtii was assessed and quantified using analytical thin-layer chromatography followed by fluorescence measurements. These data reveal that photoperiod had a significant influence on the processes and mechanisms studied in C. reinhardtii. Moreover, MLT had the greatest impact on C. reinhardtii under conditions promoting photo-oxidative stress. Addition of MLT to the growth medium down-regulated carotenoid content and the expression of FeSOD and MnSOD. These results support the idea that MLT has a physiological role as a direct and indirect antioxidant agent.