Spermidine enhanced resistance of Chlorella to high levels of CO2 and light intensity for improving photosynthetic growth rate

In order to promote the photosynthetic growth rate of Chlorella in the presence of flue gas CO2 from coal-fired power plants, spermidine was first used to enhance cellular resistance to a high CO2 concentration (15%) and high light intensity (30 000 lux). It was found that low concentrations (100-300 mu M) of spermidine significantly enhanced the photosynthetic growth rate of Chlorella. The accelerated cell division decreased the cell diameter from 3.64 mu m to 2.71 mu m and the fractal dimension from 1.60 to 1.49, and the activity of total superoxide dismutase (T-SOD) increased from 0.48 U mL(-1) to 5.33 U mL(-1). Expression levels of key enzymes of photosystems I and II, ATP synthase and transportase markedly increased, thereby enhancing the electron transport and energy supply that reduced oxidative damage. Finally, an enhanced cellular resistance to the high CO2 concentration and high light intensity increased the biomass yield from 0.11 g L-1 to 1.71 g L-1 (300 mu M).