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How plants tell time - Dasha Savage

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    In the 18th Century,
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    Swedish botonist Carolus Linnaeus
    designed the flower clock,
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    a timepiece made of flowering plants
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    that bloom and close
    at specific times of day.
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    Linnaeus' plan wasn't perfect,
    but the idea behind it was correct.
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    Flowers can indeed sense time,
    after a fashion.
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    Mornings glories unfurl their petals
    like clockwork in the early morning.
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    A closing white water lily
    signals that it's late afternoon,
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    and moon flowers, as the name suggests,
    only bloom under the night sky.
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    But what gives plants
    this innate sense of time?
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    It's not just plants, in fact.
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    Many organisms on Earth
    have a seemingly inherent awareness
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    of where they are in the day's cycle.
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    That's because of circadian rhythms,
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    the internal timekeepers
    that tick away inside many living things.
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    These biological clocks allow organisms
    to keep track of time
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    and pick up on environmental cues
    that help them adapt.
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    That's important, because the planet's
    rotations and revolutions
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    put us in a state of constant flux,
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    although it plays out in a repetitive,
    predictable way.
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    Circadian rhythms incorporate various cues
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    to regulate when an organism
    should wake and sleep,
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    and perform certain activities.
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    For plants, light and temperature
    are the cues which trigger reactions
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    that play out at a molecular scale.
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    The cells in stems, leaves, and flowers
    contain phytochromes,
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    tiny molecules that detect light.
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    When that happens, phytochromes
    initiate a chain of chemical reactions,
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    passing the message down
    into the cellular nuclei.
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    There, transcription factors trigger
    the manufacture of proteins
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    required to carry out
    light-dependent processes,
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    like photosynthesis.
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    These phytochromes not only sense
    the amount of light the plant receives,
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    but can also detect tiny differences
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    in the distribution of wavelengths
    the plant takes in.
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    With this fine tuned sensing,
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    phytochromes allow the plant
    to discern both time,
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    the difference between
    the middle of the day and the evening,
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    and place, whether
    it is in direct sunlight or shade,
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    enabling the plant to match
    its chemical reactions to its environment.
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    This makes for early risers.
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    A few hours before sunrise,
    a typical plant is already active,
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    creating MRNA templates
    for its photosynthesizing machinery.
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    As the phytochromes
    detect increasing sunlight,
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    the plant readies
    its light-capturing molecules
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    so it can photosynthesize
    and grow throughout the morning.
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    After harvesting their morning light,
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    plants use the rest of the day
    to build long chains of energy
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    in the form of glucose polymers,
    like starch.
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    The sun sets, and the day's work is done,
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    though a plant is anything
    but inactive at night.
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    In the absence of sunlight,
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    they metabolize and grow,
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    breaking down the starch from
    the previous day's energy harvest.
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    Many plants have seasonal rhythms as well.
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    As spring melts the winter frost,
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    phytochromes sense the longer days
    and increasing light,
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    and a currently unknown mechanism
    detects the temperature change.
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    These systems pass the news
    throughout the plant
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    and make it produce blooming flowers
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    in preparation for the pollinators
    brought out by warmer weather.
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    Circadian rhythms act as link
    between a plant and its environment.
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    These oscillations come
    from the plants themselves.
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    Each one has a default rhythm.
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    Even so, these clocks
    can adapt their oscillations
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    to environmental changes and cues.
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    On a plant that's in constant flux,
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    it's the circadian rhythms that enable
    a plant to stay true to its schedule
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    and to keep its own time.
Title:
How plants tell time - Dasha Savage
Description:

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Video Language:
English
Team:
closed TED
Project:
TED-Ed
Duration:
04:20

English subtitles

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