Chlorella ellipsoidea Gerneck (IAM C-27) was synchronously grown and cells at an intermediate stage in the ripening phase of the cell cycle were hardened at 3 C for 48 hours. At various times of hardening, the cells were pulse-labeled for 4 minutes with [14C]NaHCO3 in the light or with [14C]glucose in the dark, and the incorporation rate of 14C into total lipids was determined. A high incorporation rate of [14C]NaHCO3 at zero time of hardening decreased after 6 hours. In the next 15 hours, a distinct increase was noted. This increase occurred prior to the development of frost hardiness. Cycloheximide completely inhibited both the increase and the development, and 3-(3,4-dichlorophenyl)-1,1-dimethylurea remarkably lowered the high incorporation rate at zero time. The incorporation rate of [14C]glucose increased along with hardiness in the dark. These results suggest that the major site of lipid synthesis shifts from chloroplasts to a cytoplasmic system during hardening of Chlorella.
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