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D Mergenhagen

Publications and source records attributed to D Mergenhagen.

16 recordsLinked to original sources
PubMed1994

High-resolution measurement of circadian periodicities in Acetabularia.

Well-expressed endogenous circadian rhythms in Acetabularia acetabulum were spectrally analyzed and recorded in time-period distributions. The stability of the circadian periods under constant conditions and their changes could be monitored continually in step sizes close to the circadian period length. The resolution of period estimates of the circadian component was increased by a factor of approximately 4-10 by adapting analyzed interval lengths to full period sizes of the corresponding main component. Methodological aspects of the applied algorithms are discussed by means of examples that measure the temperature dependency of the circadian period.

Acetabularia↗
PubMed1989

The expression of a circadian rhythm in two strains of Chlamydomonas reinhardii in space.

During the D1 mission the endogenous circadian rhythm of the photoaccumulation response persisted in two strains of Chlamydomonas. The amplitude was about twice as high in space as on the ground indicating that a larger fraction of cells was able to contribute to the expression of the rhythm. On the ground, cells usually enter the light cone of the illuminated area in the recording cuvette on the upper edge and leave it, due to gravity, on the lower one in a pulsating manner. This sometimes produces high frequency oscillations of light extinction on the ground. In space there were no such fluctuations; instead, cells swam into the light and stayed there harvesting more light energy for photosynthesis than did control cells. This probably enhanced the survival rate and increased the fraction of motile cells which contribute to the photoaccumulation. A more sophisticated evaluation technique allowed determination of the phase in the short period strain; it was delayed by two hours compared to the control. In an acetate free wildtype sample a rhythm with a period of about 24 hours was also detected.

Animals↗
PubMed1987

The biological clock of Chlamydomonas reinhardii in space.

The overt circadian rhythm in a wildtype (wt+) and a short period (s-) strain of Chlamydomonas reinhardii has been studied in space using the photoaccumulation behavior as the recorded parameter. The period of the wt+ was 29.6 h, of the s- 21.4 h and did not deviate significantly from ground controls performed exactly at the same time. The phase was delayed in space by 4.2 h in the wt+, but was not altered in the s-. In both strains the amplitudes were significantly higher in space than in the ground controls. During the recording period of 6.5 days the cell density increased in both strains. The survival rate, i.e. the ability to form colonies on agar petri dishes, was higher in space than on ground. The period was in both strains by 1.1 h longer in Florida (Kennedy Space Center) in both the flight and the control samples than in Europe. The significance of these results is discussed with respect to the endogenous nature of the biological clock and the role of the microgravity environment.

Cell Division↗
PubMed1984

Circadian clock: genetic characterization of a short period mutant of Chlamydomonas reinhardii.

The periods in wildtype (25 hours) and short period mutant (18 hours) of Chlamydomonas reinhardii show substantial fluctuations. Due to the considerable difference between both period types of more than 6 hours the frequency distributions of the period recordings obtained from both strains are sufficiently well separated. Crosses between both strains give rise to a progeny consisting of the short as well as the wildtype period. In about 30% of the zygotes one of the daughter strains does not show any rhythmicity and is called arrhythmic. The role of arhythmicity in the genetic representations of short and wildtype period is discussed in detail.

Biological Clocks↗
PubMed1976

Membranes and molecules in circadian systems.

A membrane clock model involving ions and ion transport is compatible with the limit cycle concept, biochemical studies, and the idea of phase shifting by ion gating. It provides an explanation for temperature compensation, and, by assuming that oscillating ion concentrations regulate the many different biochemical and physiological rhythms, it explains how diverse systems can be controlled by a single oscillatory mechanism. How ions control ion transport and which membranes are involved in the clock are two questions we have begun to explore.

Animals↗