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SENSITIVE WINDOW. "Light received during the photoinducible phase (dawn or an night break) prevents the short day response. Thus it is easy to think that the circadian rhythm in light sensitivity provides the timing base that allows the length of the dark period to be distinguished by the plant." https://lnkd.in/d_f7kfY View in LinkedIn

DUSK SIGNAL. "Short day plants often exhibit a qualitative requirement for inductive photoperiods and can frequently be induced to flower in response to a single inductive light–dark cycle. In such plants the circadian rhythm of responsiveness to night breaks is entrained by the dusk signal, so that the photoinducible phase always occurs at about the same time in darkness." https://lnkd.in/d_f7kfY View in LinkedIn

NIGHT BREAKS. "Responsiveness to night breaks was rhythmic in short day species and oscillated with a period of approximately 24 h. Results obtained with long day plants also supported this model, but suggested that the characteristics of the interaction of light and circadian rhythms were not the same in short day plants and long day plants." https://lnkd.in/d_f7kfY View in LinkedIn

"THE TIMING MECHANISM used in photoperiodism seems in most cases to be based on endogenous circadian rhythms in light sensitivity, as first postulated by Bunning (1936). He suggested that the circadian clock consisted of two half cycles, photophil and scotophil. When light was received in the scotophilic phase, the daily cycle was perceived as an long day, but the absence of light during the scotophilic phase produced an short day response. Support for these circadian clock-based models was initially provided by physiological studies." https://lnkd.in/d_f7kfY View in LinkedIn

ENTRAINMENT BY PHOTORECEPTORS. "Synchronization of circadian clocks to light–dark cycles (often described as entrainment) is mediated by the action of multiple photoreceptors. In Arabidopsis, this includes at least four of the five phytochromes." https://lnkd.in/d_f7kfY View in LinkedIn

CIRCADIAN CHARACTERISTICS. "These rhythms all share the same fundamental properties: (i) their ability to become entrained, or synchronized, to diurnal changes in environmental conditions; (ii) persistence upon transfer to constant conditions; and (iii) a constant period over the physiological range of temperatures." https://lnkd.in/d_f7kfY View in LinkedIn

INTERLOCKING LOOPS. "Evidence is accumulating that the plant circadian clock comprises additional interlocking feedback loops, similar to those described in animal and fungal clocks." https://lnkd.in/d_f7kfY View in LinkedIn

TRANSCRIPTION PRESENCE. "Circadian control of transcription is widespread, and the list of plant genes regulated by the circadian clock is extensive. Microarray analyses suggest that ∼10% of all Arabidopsis genes regulated at the level of mRNA abundance and have identified multiple metabolic pathways under circadian control." https://lnkd.in/d4JRQbh View in LinkedIn

CLOCK CYCLE. "Accumulation of the TOC1 protein at night promotes transcription from the LHY and CCA1 promoters, thus initiating a new cycle." https://lnkd.in/d_f7kfY View in LinkedIn

FRAGMENT FROM NATURE continues for the second of three weekends on the theme of plant clocks, why they exist, and how they work. These mechanisms are ubiquitous across taxa, and are sophisticated in construction. In many (or most) cases, when external stimuli are removed, they keep ticking. Living things, it seems, are obsessed with time, and have put a lot of ingenuity into marking its passage. I shall refrain from quoting TS Eliot. View in LinkedIn