Physiological responses of the green microalgaAcutodesmus dimorphusto temperature induced oxidative stress conditions

Temperature is the most critical factor that directly affects the physiological functioning and metabolic activities of any organism. With rising global temperature, understanding the heat stress response of an organism is critically important. In the present study, we investigated differences in the early changes occurring upon heat stress in the green microalgaAcutodesmus dimorphus, a potential strain for biofuel production. The cells were heat-stressed at 45 and 50 degrees C for 24 h and the temporal response of cells in terms of growth, pigments content, levels of oxidative stress biomarkers i.e., reactive oxygen species (ROS) and the response of enzymatic and non-enzymatic antioxidant scavengers were evaluated. The results revealed that after 24 h of heat stress at 45 degrees C, the accumulations of chlorophyllaand carotenoids remained stable; all three ROS increased with the higher activities of various enzymatic and non-enzymatic antioxidants. On the contrary, at a higher temperature of 50 degrees C, the accumulations of chlorophylla, carotenoids and non-enzymatic antioxidants reduced drastically while the accumulations of all three ROS and the response of enzymatic antioxidants were significantly higher than those at 45 degrees C. These results suggest that the cells utilize several stress acclimatization mechanisms to cope up the heat stress. There was a dramatic difference in the physiological changes and cellular antioxidant mechanism upon heat stress at 45 and 50 degrees C. The cellular defense response ofA. dimorphusgets impaired after heat stress at 50 degrees C but remains active at 45 degrees C, exhibiting the heat resistance and, thus, the thermotolerance.