Unlike plants and animals, the phytoflagellate lacks catalase and contains a non-selenocysteine glutathione peroxidase-like protein (EgGPXL), two peroxiredoxins (EgPrx1 and EgPrx4), and one ascorbate peroxidase in the cytosol to maintain reactive oxygen species (ROS) homeostasis. In the present study, the full-length cDNA of three cytosolic EgGPXLs was obtained and further characterized biochemically and functionally. These EgGPXLs used thioredoxin instead of glutathione as an electron donor to reduce the levels of HO and -BOOH. The specific peroxidase activities of these enzymes for HO and -BOOH were 1.3 to 4.9 and 0.79 to 3.5 µmol/min/mg protein, respectively. Cytosolic s and / were silenced simultaneously to investigate the synergistic effects of these genes on the physiological function of . The suppression of cytosolic genes was unable to induce any critical phenomena in under normal (100 μmol photons m s) and high-light conditions (350 μmol photons m s) at both autotrophic and heterotrophic states. Unexpectedly, the suppression of genes was able to rescue the -silenced cell line from a critical situation. This study explored the potential resilience of to ROS, even with restriction of the cytosolic antioxidant system, indicating the involvement of some compensatory mechanisms.