. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 40 60 80 TIME - HOURS 100 120 140 FIGURE 4. The initiation of an endogenous diurnal rhythm of luminescence by means of a one-step change in illumination. Cultures which had been grown in bright light for one year were moved from bright light (800 foot-candles) to dim light (90 foot-candles) at the time indicated on the graph as 0 hours. Luminescence measurements were made approximately every two hours thereafter. Temperature, ° C. Average period, hours. illustrated in Figure 4. It differs from the previously mention
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 40 60 80 TIME - HOURS 100 120 140 FIGURE 4. The initiation of an endogenous diurnal rhythm of luminescence by means of a one-step change in illumination. Cultures which had been grown in bright light for one year were moved from bright light (800 foot-candles) to dim light (90 foot-candles) at the time indicated on the graph as 0 hours. Luminescence measurements were made approximately every two hours thereafter. Temperature, ° C. Average period, hours. illustrated in Figure 4. It differs from the previously mentioned experiment (in which cultures were moved from bright light to darkness) in that the ampli- tude does not decrease with time, since light is available for the nutrition of the cells. The precise phase relationship to the time of transfer from bright light is somewhat different, but here also it is not related to solar time. Phase shift by light perturbation. It is clear from Figure 2 that the phase of the rhythm may readily be shifted by an appropriate manipulation of the light and dark periods to which the cells are exposed. It is not necessary, however, to expose the cells to a new light-dark cycle in order to reset the phase of the rhythm. A single exposure to a different light intensity can result in a stable phase shift. Pittendrigh and Bruce (1957) have discussed the significance of phase resetting of biological rhythms by single light perturbations. If rhythmicity results from an innate oscillatory mechanism characterized by its own natural period, and the phase (but not the period) is determined by the sequence of light and darkness, then it is to be expected that non-repeated light changes should suffice to change the phase. The perturbation therefore need not contain any information concerning period. The experiment shown in Figure 4 illustrates phase setting by a single step- type light perturbation. The phase of the previously aperiodic cells was deter- mined by
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
