Plastid terminal oxidases (PTOXs) are essential for maintaining photosynthetic efficiency and cellular redox homeostasis. Astaxanthin, a carotenoid pigment with antioxidant properties, is synthesized and accumulates in response to oxidative stress induced by high-light intensity or nutrient limitation. It suggests that PTOX may impact astaxanthin biosynthesis under environmental stress conditions due to its involvement in ROS regulation. The ptox1 gene is thought to have a conserved role in safeguarding the photosynthetic apparatus from over-reduction and participating in energy dissipation. On the other hand, the ptox2 gene seems to be involved in the evolution of astaxanthin synthesis and adaptive responses to diverse environmental stressors. Efficient gene silencing strains were developed in Chlamydomonas reinhardtii CC849 for ptox1 and ptox2. The study found that the ptox2 gene correlates highly with resistance to intense light stress. Furthermore, the ptox2 gene showed increased activity under high salt stress conditions, indicating its importance in stress coping mechanisms. The quantification of astaxanthin in the gene-silenced strains revealed that ptox1 acts as a positive regulator, while ptox2 functions as a negative regulator of astaxanthin accumulation. Understanding the coordination between ptox1 and ptox2 could clarify the synergistic actions of these genes in maintaining photosynthetic performance and redox balance under fluctuating environmental conditions.