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In plant biology, nyctinasty is the circadian rhythm-based nastic movement of higher plants in response to the onset of darkness, or a plant "sleeping". Nyctinastic movements are associated with diurnal light and temperature changes and controlled by the circadian clock.
Linnaeus's flower clock was a garden plan hypothesized by Carl Linnaeus that would take advantage of several plants that open or close their flowers at particular times of the day to accurately indicate the time. [1] [2] According to Linnaeus's autobiographical notes, he discovered and developed the floral clock in 1748. [3]
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).
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.
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.
Animal Cry can be further categorized into insect type (Type I) and mammal-like (Type II). CRY1 is a circadian photoreceptor whereas CRY2 is a clock repressor which represses Clock/Cycle (Bmal1) complex in insects and vertebrates. [4] In plants, blue-light photoreception can be used to cue developmental signals. [5]
The uniform alignment of the flowers does result from heliotropism in an earlier development stage, the bud stage, before the appearance of flower heads. The apical bud of the plant will track the Sun during the day from east to west, and then will quickly move west to east overnight as a result of the plant's circadian clock. [11]
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.