Effects of Low Temperature, Light and O<sub>2</sub> on Chilling-sensitive and -resistant Strains in <italic>Chlorella ellipsoidea</italic>

Abstract

A low-temperature sensitive strain, Chlorella ellipsoidea Gerneck (IAM C-102), lost its chilling sensitivity during preservation. Cells of the original strain (low-temperature sensitive) and the variant (low-temperature resistant) were both synchronously grown under a 14-hr light-10-hr dark regime. In the original strain, cells at the D-L stage (transient phase) were most sensitive to a low temperature, whereas the variant cells were not damaged at any stage. During low-temperature treatment, the viability of D-L cells in the sensitive strain decreased after a lag period of 1 hr. The O2-uptake activity (respiration) showed the same behavior as the viability, whereas the O2-evolution activity (photosynthesis) decreased from the start of chilling. In the resistant strain, only O2 evolution decreased. The decreased activity was restored when the chilled cells were incubated at 25°C. This restoration was inhibited by oligomycin. Lowering the light intensity or eliminating O2 diminished the chilling injury of the sensitive strain. The results indicate that the chilling injury of Chlorella results from the combined effects of low temperature, light and O2.