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CAB is confined to the mesophyll and guard cells and the cycling of CAB expression in the Arabidopsis plant suggests that there is a circadian clock that controls the CAB gene. [ 16 ] [ 17 ] When the plants were moved from light/dark cycles to constant darkness, CAB2 and CAB3 genes showed an exaggerated circadian cycling. [ 17 ]
The circadian clock in plants has completely different components to those in the animal, fungus or bacterial clocks. The plant clock does have a conceptual similarity to the animal clock in that it consists of a series of interlocking transcriptional feedback loops. The genes involved in the clock show their peak expression at a fixed time of day.
The TOC1 gene was initially discovered by Prof. Andrew Millar and colleagues in 1995 while Millar was a graduate student. Millar developed an innovative forward genetic screen in which he linked a bioluminescent reporter, firefly (), to expression of CAB (chlorophyll-a,b binding protein—see Light-harvesting complexes of green plants) in Arabidopsis.
Circadian Clock Associated 1 (CCA1) is a gene that is central to the circadian oscillator of angiosperms. It was first identified in Arabidopsis thaliana in 1993. CCA1 interacts with LHY and TOC1 to form the core of the oscillator system.
The morning loop consists of CCA1 (Circadian and Clock-Associated 1) and LHY (Late Elongated Hypocotyl), which encode closely related MYB transcription factors that regulate circadian rhythms in Arabidopsis, as well as PRR 7 and 9 (Pseudo-Response Regulators.) The evening loop consists of GI (Gigantea) and ELF4, both involved in regulation of ...
In vertebrates, the master circadian clock is contained within the suprachiasmatic nucleus (SCN), a bilateral nerve cluster of about 20,000 neurons. [10] [11] The SCN itself is located in the hypothalamus, a small region of the brain situated directly above the optic chiasm, where it receives input from specialized photosensitive ganglion cells in the retina via the retinohypothalamic tract.
In the study of chronobiology, entrainment refers to the synchronization of a biological clock to an environmental cycle. An example is the interaction between circadian rhythms and environmental cues, such as light and temperature. Entrainment helps organisms adapt their bodily processes according to the timing of a changing environment. [1]
The best studied rhythm in chronobiology is the circadian rhythm, a roughly 24-hour cycle shown by physiological processes in all these organisms. The term circadian comes from the Latin circa, meaning "around" and dies, "day", meaning "approximately a day." It is regulated by circadian clocks.