Rhythmicity and oxidative/nitrosative stress in algae

We review here the evidence linking molecular control of the biological clocks to the cellular toxicity and the generation of ROS/RNS (reactive oxygen species/re active nitrogen species) in algae. A discussion is also made of the possible relevant relationships between the rhythmicity of photosynthetic activity (particularly insofar as it concerns the circadian fluctuations of light-absorbing pigments and chlorophyll a/b binding proteins), nitrate reductase (a potential NO source in algae and higher plants under specific circumstances) and major antioxidant enzyme activities, aiming to gain a better understanding of the oscillatory levels of oxidative/nitrosative modifications in algal cells. A comparison is also made of the biosynthesis of low molecular weight antioxidants such as carotenoids, melatonin, reduced gluthatione, mycosporine-like amino acids and ROS targets, such as polyunsaturated fatty acids, and the biological clocks and oxidative stress.