Figure 4.

Respiration rates of R. litoralis cells. A: exponential growth phase; B: stationary growth phase. The values in mV min^-1 indicate the respiration rates in the respective time intervals. Cells were kept anoxic under nitrogen gas until oxygen was supplied. At the beginning of each respiration measurement the cell suspension was saturated with oxygen and the oxygen consumption of the cells was measured in mV min^-1. The response of R. litoralis to light differs remarkably between the two growth phases. During the exponential growth phase the initial respiration rate in the dark was higher (220 mV min^-1) than in the stationary growth phase (140 mV min^-1). When exposed to light, the cells that were in the exponential growth phase showed only a slight decrease to 200 mV min^-1 (10%) of the respiration rate whereas in the stationary phase culture the respiration rate was reduced to 43% (60 mV min^-1) of the original rate in the first light period and to 25% (30 mV min^-1) in the second. Cells resumed 95% (exponential growth phase) and 86% (stationary growth phase) of their original respiration rate when darkened again.