How plants tell time - Dasha Savage

by Panzer
In the 18th century,
Swedish botanist Carolus Linnaeus designed the flower clock,
a timepiece made of flowering plants
that bloom and close at specific times of day.
Linnaeus's plan wasn't perfect, but the idea behind it was correct.
Flowers can indeed sense time, after a fashion.
Mornings glories unfurl their petals like clockwork in the early morning.
A closing white water lily signals that it's late afternoon,
and moon flowers, as the name suggests, only bloom under the night sky.
But what gives plants this innate sense of time?
It's not just plants, in fact.
Many organisms on Earth have a seemingly inherent awareness
of where they are in the day's cycle.
That's because of circadian rhythms,
the internal timekeepers that tick away inside many living things.
These biological clocks allow organisms to keep track of time
and pick up on environmental cues that help them adapt.
That's important, because the planet's rotations and revolutions
put us in a state of constant flux,
although it plays out in a repetitive, predictable way.
Circadian rhythms incorporate various cues
to regulate when an organism should wake and sleep,
and perform certain activities.
For plants, light and temperature are the cues which trigger reactions
that play out at a molecular scale.
The cells in stems, leaves, and flowers contain phytochromes,
tiny molecules that detect light.
When that happens, phytochromes initiate a chain of chemical reactions,
passing the message down into the cellular nuclei.
There, transcription factors trigger the manufacture of proteins
required to carry out light-dependent processes,
like photosynthesis.
These phytochromes not only sense the amount of light the plant receives,
but can also detect tiny differences
in the distribution of wavelengths the plant takes in.
With this fine-tuned sensing,
phytochromes allow the plant to discern both time,
the difference between the middle of the day and the evening,
and place, whether it is in direct sunlight or shade,