1. Introduction
A circadian rhythm is a biological process which shows an endogenous and entrainable oscillation of about 24 h. These 24-h rhythms are regulated by a circadian clock and are widely displayed in different organisms, including plants, fungi, animals, and cyanobacteria [1]. The endogenous circadian rhythms are adjusted to the environment by different surrounding cues, such as temperature, light, and redox cycles. In 2017, Jeffrey C. Hall and his colleagues have awarded the Nobel Prize in Physiology or Medicine for their discoveries of molecular mechanisms controlling the circadian rhythm. Circadian system runs as a result of four main components: (i) photosensitive retinal neurons and retinohypothalamic tract through which light signals come from the environment, (ii) internal circadian oscillator, generating rhythms and synchronizing them with the environment, (iii) signal paths transmitting information from the central regulator to peripheral rhythm generators, and (iv) peripheral rhythm generators (clock genes and proteins in peripheral cells).
In 1729, the French scientist Jean-Jacques d’Ortous de Mairan reported the first observation of an endogenous circadian oscillation and found that 24-h patterns in the movement of the leaves of the plant species
2. Importance and molecular mechanisms of circadian rhythms
Circadian rhythms enable organisms to better prepare and capitalize on environmental factors (e.g., light and food) as compared to those that are not able to predict such availability. They are also important in regulating and coordinating internal physiological processes [16]. Photoperiodism, the physiological reaction of organisms to the length of day or night, is essential to both plants and animals, and the circadian system plays a crucial role in the measurement of day length. The rhythm is linked to the light-dark cycle. Plant circadian rhythms tell the plant what season it is and when to flower to better attract pollinators. A better understanding of plant circadian rhythms has applications in agriculture, such as helping farmers to extend crop availability and secure it against massive losses due to weather. In addition,
References
- 1.
Edgar RS, Green EW, Zhao Y, van Ooijen G, Olmedo M, Qin X, Xu Y, Pan M, Valekunja UK, Feeney KA, Maywood ES, Hastings MH, Baliga NS, Merrow M, Millar AJ, Johnson CH, Kyriacou CP, O'Neill JS, Reddy AB. Peroxiredoxins are conserved markers of circadian rhythms. Nature. 2012; 485 :459-464 - 2.
de Mairan JJO. Observation botanique. Histoire de l'Academie Royale des Sciences. 1729; 31 :35-36 - 3.
Gardner MJ, Hubbard KE, Hotta CT, Dodd AN, Webb AA. How plants tell the time. The Biochemical Journal. 2006; 397 :15-24 - 4.
Dijk DJ, von Schantz M. Timing and consolidation of human sleep, wakefulness, and performance by a symphony of oscillators. Journal of Biological Rhythms. 2005; 20 :279-290 - 5.
Bruce VG, Pittendrigh CS. Endogenous rhythms in insects and microorganisms. The American Naturalist. 1957; 91 :179-195 - 6.
Pittendrigh CS. Temporal organization: Reflections of a Darwinian clock-watcher. Annual Review of Physiology. 1993; 55 :16-54 - 7.
Pittendrigh CS. On temperature independence in the clock system controlling emergence time in Drosophila . Proceedings of the National Academy of Sciences of the United States of America. 1954;40 :1018-1029 - 8.
Konopka RJ, Benzer S. Clock mutants of Drosophila melanogaster . Proceedings of the National Academy of Sciences of the United States of America. 1971;68 :2112-2116 - 9.
Reddy P, Zehring WA, Wheeler DA, Pirrotta V, Hadfield C, Hall JC, Rosbash M. Molecular analysis of the period locus in Drosophila melanogaster and identification of a transcript involved in biological rhythms. Cell. 1984; 38 :701-710 - 10.
Zehring WA, Wheeler DA, Reddy P, Konopka RJ, Kyriacou CP, Rosbash M, Hall JC. P-element transformation with period locus DNA restores rhythmicity to mutant, arrhythmic Drosophila melanogaster . Cell. 1984;39 :369-376 - 11.
Bargiello TA, Jackson FR, Young MW. Restoration of circadian behavioural rhythms by gene transfer in Drosophila . Nature. 1984;312 :752-754 - 12.
Bargiello TA, Young MW. Molecular genetics of a biological clock in Drosophila . Proceedings of the National Academy of Sciences of the United States of America. 1984;81 :2142-2146 - 13.
Vitaterna MH, King DP, Chang AM, Kornhauser JM, Lowrey PL, McDonald JD, Dove WF, Pinto LH, Turek FW, Takahashi JS, et al. Mutagenesis and mapping of a mouse gene, clock, essential for circadian behavior. Science. 1994; 264 :719-725 - 14.
Debruyne JP, Noton E, Lambert CM, Maywood ES, Weaver DR, Reppert SM. A clock shock: Mouse clock is not required for circadian oscillator function. Neuron. 2006; 50 :465-477 - 15.
Collins B, Blau J. Keeping time without a clock. Neuron. 2006; 50 :348-350 - 16.
Sharma VK. Adaptive significance of circadian clocks. Chronobiology International. 2003; 20 :901-919