Studies on frost hardiness in Chlorella ellipsoidea. V. The role of glucose and related compounds

Abstract

Chlorella ellipsoidea cells at an intermediate stage in the ripening phase of the life cycle were hardened at 3°C. d-Glucose added during hardening in the dark induced a tolerance to freezing. Sucrose, d-galactose and d-fructose were also capable of increasing hardiness, but pyruvate, succinate and citrate were not. These results suggest the involvement of the pentose-phosphate cycle in the hardening process. The amounts of monosaccharide and dextrin in Chlorella cells did not change during hardening. Sucrose concentration increased during hardening in both the light and the dark in the presence of glucose. Starch concentration remained unchanged in the dark in the presence of glucose, but increased remarkably in the light. These results suggest that the hardening process involves an accumulation of sucrose, and indicate that there is no direct correlation between starch content and frost hardiness. Glucose 6-phosphate dehydrogenase activity increased greatly during the early phase of hardening; 6-phosphogluconate dehydrogenase activity also increased with hardiness. These results suggest that pentose-phosphate cycle activity occurs at a high level during hardening. Cycloheximide and oligomycin completely inhibited the hardiness increase in the dark in the presence of glucose; chloramphenicol and DCMU had no effect. These results suggest that protein synthesis on cytoplasmic ribosomes and ATP synthesis in mitochondria are involved in the process of hardening in the dark in the presence of glucose, but protein and ATP synthesis in chloroplasts are not. The inhibition of the hardiness increase by sodium dodecyl sulfate was greater in the light than in the dark in the presence of glucose. Triton X-100 inhibited completely the hardiness increase in both the light and the dark in the presence of glucose. It seems likely, therefore, that membrane alterations during hardening in the dark in the presence of glucose may occur; these alterations are different from those which occur in the light.