Membrane model for the circadian clock

Njus, David; Sulzman, Frank M.; Hastings, J. Woodland

doi:10.1038/248116a0

Cited by 273 publications

(93 citation statements)

References 59 publications

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“…Therefore, an alteration of the electron transport system or some membrane change may be the mechanism by which chloramphenicol alters the circadian rhythm. The destabilization of membranes possibly caused by chloramphenicol is consistent with both Bunning's (3) Njus' (14) models that membranes are involved in the circadian rhythm.…”

Section: Discussionsupporting

confidence: 65%

Effects of Chloramphenicol on the Circadian Rhythm of Neurospora crassa

Frelinger

Motulsky²,

Woodward³

1976

Plant Physiol.

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Chloramphenicol, an inhibitor of mitochondrial protein synthesis, shortened the period length of the circadian rhythm in the Timex strain of Neurospora crassa by 2 hours. Both the L(+) threo and D(-) threo optical isomers had the same effect on the period of the rhythm, whereas only the D(-) threo isomer significantly inhibited mitochondrial protein synthesis. Tetracycline, another inhibitor of mitochondrial protein synthesis, did not change the period of the circadian rhythm. The effect of chloramphenicol on the circadian rhythm is, therefore, presumably not directly related to inhibition of mitochondrial protein synthesis, suggesting that chloramphenicol has other effects.Circadian rhythms provide one type of eucaryotic cell regulation and have been described in a variety of organisms. Despite much work, very little is known about the biochemical basis of the "biological clock." One experimental approach has been to use chemicals and drugs to alter the rhythm. Heavy water (D20) (2), ethanol (5), lithium (4), and cycloheximide (6) have all been reported to increase the period of the rhythm in at least one organism. Many biological processes are presumably affected by these chemicals, and it is, therefore, difficult to make inferences regarding the basic biological mechanism of the circadian clock from such studies. There have been no previous reports of chemicals decreasing the period of a circadian rhythm.Circadian rhythms have not been clearly demonstrated in procaroytic organisms, although all studied eucaryotic organisms do exhibit a rhythm. Because only eucaryotes have mitochondria, there has been speculation that mitochondria have a role in circadian rhythms (1). We, therefore, studied the effect of an inhibitor of mitochondrial protein synthesis, chloramphenicol, on the period of the circadian rhythm in Neurospora crassa.There are L(+) threo and D(-) threo4 optical isomers of chloramphenicol. D(-) Chloramphenicol inhibits mitochondrial protein synthesis (9, 13, 19), but L(+) chloramphenicol does not (7). In this paper, we report that both isomers of chloramphenicol decrease the period length of the circadian rhythm in Neurospora crassa as expressed by periodic conidia formation. MATERIALS AND METHODSGrowth Conditions. For these experiments, we used the Timex strain of Neurospora crassa which was isolated and characterized by Sargent et al. (15,16). Glass tubes 60 cm long and 13 mm in diameter were half filled with 18 ml of medium containing Vogel's solution (20), 0.5 % sucrose, 0.5 % casamino acids, and 1.5 % bacto agar. A chloramphenicol isomer (max. 2 mg/ml) or tetracycline (max. 0.75 mg/ml) was added to the medium after autoclaving. The chloramphenicol isomers were added directly to the medium. Tetracycline was dissolved in sterile H20 which was then added to an equal volume of double strength medium at 50 C. The tubes were inoculated at one end with conidia from a 5-day-old culture. They were then placed in a constant temperature incubator inside a darkroom and were observed thereafter only...

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Section: Discussionsupporting

confidence: 65%

Effects of Chloramphenicol on the Circadian Rhythm of Neurospora crassa

Frelinger

Motulsky²,

Woodward³

1976

Plant Physiol.

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“…The variations in Chl in each of the five individual experiments were well marked, and although they showed varying phase angles to the corresponding rhythms in PC, the composite statistical plot (Fig. 4) 24 h, whereupon circadian time 0 was ascertained by reference to the point (minimal value of the oscillation in most instances) corresponding to the onset of light in the rhythm of PC entrained by LD: 12,12 (Fig. IA).…”

Section: Resultsmentioning

confidence: 99%

Cell Cycle-related and Endogenously Controlled Circadian Photosynthetic Rhythms in Euglena

Laval-Martin

Shuch²,

Edmunds³

1979

Plant Physiol.

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The data presented for three strains of Euglena gracilis corroborate previous reports of a diel rhythm in photosynthetic capacity in divisionsynchrnized cultures of this alga and extend these studies to free nning, dividing and nondividing (stationary) Circadian rhythms in photosynthesis have been observed in a number of higher plants as well as in algae (16). Several studies have reported a rhythm of photosynthetic capacity during the cell cycle of the alga flagellate Euglena (3,4,22,32), although the results are often conflicting. Walther and Edmunds (32) demonstrated a clear 24-h rhythm in the capacity of Euglena to fix CO2 in cultures synchronized by appropriately chosen light (12,000 lux) cycles (LD: l0,14 This lack of long term persistence of the photosynthetic capacity rhythm and hence the inability to conclude that an endogenous circadian clock underlies the overt periodicity, could have been

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“…Such an investigation is desirable in view of the increasing evidence (27) that membranes are components of circadian oscillators, and the speculation that temperature-induced alterations of membrane lipid composition may be related to temperature conpensation of biological rhythms (16). In addition, there are reports (1, 7) that microwaves shift the phase of the biological clock.…”

mentioning

confidence: 99%