Changes in pigment content, lipid pattern and ultrastructure of synchronous Chlorella after heat and cold shocks.

Completely synchronous Chlorella cultures were treated with heat (45°C) or cold shocks (4° C) of different lengths at the sixth hour of the 14:10 h lightdark-cycle. After the treatment the cells were grown under normal conditions. Analysis at the end of the cycle showed a direct connection between pigment bleaching, reduction of lipid content, loss of thylakoid stacking and a shift of the fluorescence emission maximuminto a region of shorter wavelength. The thylakoid stacking was completely loosened after a heat shock while two thylakoids remained in contact after cold treatment. This probably explains the different regeneration capacities in temperature shock treated cells. None of the described effects could be observed directly after the shocks. From the parallel decay of chlorophyll a, monogalactosyl diglyceride and carotenoids an intimate correlation with the photosystem II complex is suggested.