Studies on frost hardiness inChlorella ellipsoideaIII. Changes in O2uptake and evolution during hardening and after freeze-thawing

摘要

Chlorella ellipsoideacells at an intermediate stage in the ripening phase of the cell cycle were hardened at 3°C. Oligomycin (OGM) and 3-(3,4-dichiorophenyl)-1,1-dimethylurea (DCMU) added during hardening in the light inhibited the development of frost hardiness, suggesting that mitochondria and chloroplasts were involved in the hardening process.The O2-uptake activity in unhardened cells increased during hardening in the light while the O2-evolution activity decreased, when these activities were measured at 25°C. The increase in O2uptake was suppressed by OGM and DCMU and the decrease in O2evolution was stimulated by OGM. While the algal hardiness in the dark was very limited, the addition of glucose during hardening in the dark caused a remarkable development of frost hardiness. These results suggest that mitochondria and chloroplasts closely interact at low temperature, and the former plays a principal role in the hardening process and the latter serves as substrate-donor in the light.The O2evolution in cells which survived freezing was remarkably decreased by freeze-thawing while the O2uptake was hardly affected. The freeze-injured chloroplasts were repaired during the following incubation. OGM inhibited the repair of freeze-injured chloroplasts. From the results, mitochondria seem to change their membranes into a structure hardier than chloroplasts, and ATP synthesized by mitochondria seems to be essential for the repair of freeze-injured chloroplast