ABSTRACT
It is believed that over 2.2 billion years ago, the presence of O2 in the Earth’s atmosphere was originatedduetotheevolutionofcyanobacteriaphotosyntheticactivity,whichusedthesun’senergyand watertoproducesugarswiththereleaseofO2. Since then, several organisms began to evolve an antioxidantdefensethatgivesthemthecapacitytotolerateO2 and use it for metabolic transformationandbiosynthesis(Halliwell2006,Slesaket al.2007).Consideringtherelationshipbetween aerobicorganismsandO2, it is remarkable that this molecule can be both benecial and damaging. BenecialforthereasonthatO2 is essential as electron exchanger for an efcient respiration and photosyntheticactivityanditislargelyusedforsignaltransduction;whiledamagingbecauseO2 cancausedysfunctiononcellcomponentsbyirreversiblemodicationsonDNA,proteins,sugars, andlipids.Hence,thereisabalance/imbalancebetweenbothsides,whichiscriticalforthecell functionality and survival (Slesak et al. 2007).
