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E Bünning

Publications and source records attributed to E Bünning.

11 recordsLinked to original sources
PubMed1978

[Evolution of the circadian organization (author's transl)].

The evolution of cicadian rhythmicity was possible by selection and mutation. Rhythms which strongly deviate from the circadian rhythms are still existent in case no selective pressure has occurred. An evoluution regressive to those strongly deviating rhythmus can be observed in case the selective pressure has disappeared. The circadian rhythmicity in the various cells and organs of multicellular organisms has not got lost during the evolution. But certain organs have grown important for maintaining the circadian organization within the body and for allowing the synchronization with the light-dark cycles. In addition, contrary to lower organisms, certain processes, e. e. photoreception, are coupled to the circadian rhythm only in specially differentiated organs. The high precision in the clock's running within higher organisms becomes possible by mutual synchronization within the multioscillator system.

Biological Clocks↗
PubMed1973

Light-induced phase shifts of circadian leaf movements of phaseolus: comparison with the effects of potassium and of ethyl alcohol.

Leaves of Phaseolus coccineus were exposed to high concentrations of KCl (0.1-0.3 M) for periods of 4-5 hr, or to ethyl alcohol (5-30%) for periods of 2 hr. The treatment started at various phases of the free-running circadian rhythm in continuous light. Whereas the K(+) pulses induced only advance phase shifts, i.e., shortening of the periods, the alcohol pulses caused stronger advances and also slight delays, i.e., lengthening of the periods. These delays became stronger with lower concentrations of alcohol (1.7%) applied for a longer time. The lengthening effect by alcohol supplied continuously depends on the intensity of light. The rather high intensity of 3500 lux, resulting in very long free-running periods of about 29 hr, inhibits a further strong lengthening by alcohol. The phases reacting with advances to K(+) and to alcohol are about the same phases that respond to light pulses with advances. The advances are reached at earlier phases of the circadian cycle when the concentration of alcohol or the strength of the light pulse is increased. The phases that respond with advances are those which, according to earlier publications, are within the energy-independent part of the cycle. The phases responding with delays belong to the energy-requiring part of the cycle. Consequently, it is suggested that advances are due to accelerated membrane depolarization and delays are due to stabilizing effects on membranes.

Journal Article↗
PubMed1972

Influence of valinomycin on circadian leaf movements of Phaseolus.

Phaseolus coccineus was exposed to valinomycin via the transpiration stream for 5-hr periods. The treatment started at various phases of the free-running circadian rhythm in continuous light; it resulted in phase shifts that varied in a manner dependent on the affected phases. The response curves are similar to those for transient withdrawal of water and for light pulses. The results support the hypothesis that membrane processes are important pacemakers in circadian rhythms.

Anti-Bacterial Agents↗
PubMed1969

Interference of moonlight with the photoperiodic measurement of time by plants, and their adaptive reaction.

Threshold values of photoperiodic time-measurements correspond approximately to moonlight intensities. Experiments with Glycine and Euglena reveal that this is also the threshold value for synchronization of the circadian cycle. Saturation of this reaction is reached with 10 lx in 12:12 hr light-dark cycles. Thus, moonlight might disturb time measurement.In Glycine, Arachis, and Trifolium the intensity of the light coming from the moon to the upper surface of the leaf is reduced by circadian leaf movement to values between 5 and 20 per cent (or even less than 5 per cent) of full-moon light intensity. Such a reduction eliminates the disturbing effects of moonlight. This finding indicates that leaf movements have an adaptive value of the kind that Darwin sought to identify. It also indicates that the behavior of the upper leaf epidermis as a "sense organ for light"(13) has an adaptive value.In the short-day plants Perilla ocymoides and Chenopodium amaranticolor, a specific photoperiodic phenomenon was found that counteracts the disturbing effect of moonlight. Here light intensities similar to those of moonlight, introduced during the night, promote flowering instead of inhibiting it.

Journal Article↗