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