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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.
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]
EARLY FLOWERING 3 (ELF3) is a plant-specific gene that encodes the hydroxyproline-rich glycoprotein and is required for the function of the circadian clock. [1] ELF3 is one of the three components that make up the Evening Complex (EC) within the plant circadian clock, in which all three components reach peak gene expression and protein levels at dusk. [2]
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.
A better understanding of plant circadian rhythms has applications in agriculture, such as helping farmers stagger crop harvests to extend crop availability and securing against massive losses due to weather. Light is the signal by which plants synchronize their internal clocks to their environment and is sensed by a wide variety of photoreceptors.
A circadian cycle was first observed in the 18th century in the movement of plant leaves by the French scientist Jean-Jacques d'Ortous de Mairan. [5] [6] In 1751 Swedish botanist and naturalist Carl Linnaeus (Carl von Linné) designed a flower clock using certain species of flowering plants. By arranging the selected species in a circular ...
The conception of the plant biological clock as made up of interacting negative feedback loops is unique in comparison to mammal and fungal circadian clocks which contain autoregulatory negative feedback loops with positive and negative elements [6] (see "Transcriptional and non-transcriptional control on the Circadian clock page).