Studies on the S-State Distribution in Euglena gracilis

Abstract

When Euglena gracilis is dark adapted for 10 min or more, oxygen evolution as the consequence of short (5 μsec) saturating light flashes does not show the picture of a damped oscillation with a periodicity of 4, as known from the literature. The overall picture of this flash pattern is given by the fact that O2-evolution in the first two flashes is practically zero and rises from there onward in a continuous manner to the steady state with barely any visible oscillation at all. However, a second flash sequence fired one to two minutes after this first sequence induces an oxygen evolution pattern which is barely distinguishable from the well known usual Chlorella vulgaris pattern. The phenomenon is not influenced by changes in the oxygen tension nor do additions of chemicals like CCCP, sodium azide, or reducing agents like hydroxylamine or hydrogen peroxide substantially alter the described behavior. Deactivation experiments give the overall impression that the deactivation of the S-states is slower than with Chlorella. Hydroxylamine strongly accelerates the deactivation. The analysis of the S-state distribution in a four and five state Kok-model suggests that dark adapted Euglena is in a more reduced condition than dark adapted Chlorella. It looks as if dark adapted Euglena were in a condition which would correspond to 60 percent S-1, 30 percent S0 and 10 percent S1. The experimental flash sequence of such dark adapted cells fits best a synthetic sequence when the misses are in the region of 20-25 percent, with double hitting playing practically no role at all (the first two flashes are zero!). The impression that dark adapted Euglena starts its oxygen evolution from a more reduced state is strengthened by the analysis of room temperature fluorescence induction (Kautsky effect). It can be shown that the fluorescence induction curve of Euglena corresponds to that of Chlorella cells provided the latter have been briefly treated with a strong reductant such as sodium dithionite.