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.
Institute of Biology, University of Tübingen, D-74 Tübingen, Federal Republic of Germany.
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Bünning
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Moser