Figure 2. Localization of a singularity point in the behavior of the CO underlying the free-running rhythm of cell division in cultures of photoautotrophically grown Euglena gracilis (Z) perturbed by a “critical” 3-h light signal.

Figure 2

Localization of a singularity point in the behavior of the CO underlying the free-running rhythm of cell division in cultures of photoautotrophically grown Euglena gracilis (Z) perturbed by a “critical” 3-h light signal. Three initially in-phase, synchronously dividing cultures were utilized, each displaying a stable τ of approximately 30 h in an LD:3,3 regimen. At Circadian Time (CT) 0.4, Culture A was perturbed by a 3-h light signal of 700 lx, while Culture B was perturbed by a 3-h light signal of only 300 lx (each replacing one of the normal light intervals in the imposed LD cycle having an intensity of 7500 lx, as represented by the hatched arrows). Whereas the former signal elicited a phase shift (ΔΦ) of +11.2 h (modulo 24) CT (equivalent to 14.0 h real time) comparable to that seen for 7500-lx light signals, the latter, weaker light pulse (Curve B) induced total arrhythmicity, although cell division continued in the population. If a third culture (Curve C) were perturbed by a 3-h signal with an identical intensity of 300 lx but imposed at a slightly different circadian time (CT21.5), the cell division rhythm continued although its phase was delayed (ΔΦ = -8.0 h CT, equivalent to -10.0 h real time) in a manner observed for 7500-lx pulses. Reprinted with permission from: Malinowski JR, Laval-Martin DL, Edmunds Jr LN. J Comp Physiol B 1985; 155:257-267. © Springer-Verlag.

From: Circadian Organization in the Algal Flagellate Euglena

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