The Effects of Temperature on86Rb Uptake by Two Species ofChlamydomonas(Chlorophyta, Chlorophyceae)

86Rb uptake was examined in two species of unicellular green algae, Chlamydomonas nivalis isolated from snow, and a cell wall-less mutant of the temperate freshwater Chlamydomonas reinhardii. In C. reinhardii cells grown at 20°C and cooled rapidly to 0°C, 86Rb uptake was abolished. Cells cooled rapidly to −5°C in the absence of ice accumulated 86Rb very rapidly but the time course of this uptake suggested non-selective accumulation through a damaged plasmalemma. Cells grown at 8°C were viable, able to divide and motile; they showed no signs of cold-shock and 86Rb uptake, albeit slow, was measurable at −5°C in the absence of extracellular ice. Cells of C. nivalis grown at 20°C were damaged at sub-zero temperatures although they did show an enhanced 86Rb uptake at 0°C. Cells grown at 5°C were able to accumulate 86Rb from media undercooled to -5°C in the absence of extracellular ice, and again showed enhanced uptake at 0°C. The process of acclimation to low temperature appears to differ in the two species.