Can Plants Tell Time?
Excerpted from Researchers show how plants tell time
Circadian rhythms are biological cycles with a period of around 24 hours, which can be thought
of as an internal clock. The prolificacy of this biological process highlights its importance to
Plants are sessile organisms (fixed in one place) and thus unable to escape when
environmental conditions become unfavorable. Circadian rhythms allow plants to cope with
adverse surroundings, as well as to synchronize themselves with predictable changes, such
as the change from day to night.
This biological timer gives plants an innate ability to measure time, even when there is no light -
they don’t simply respond to sunrise, for example, they know it is coming and adjust their biology
This ability to keep time provides an important competitive advantage and is vital in biological
processes such as flowering, fragrance emission and leaf movement.
Signals from the environment such as light and temperature that help to keep the internal
plant's clock in sync with the environment. This synchronization is known as entrainment.
Researchers studying how plants are able to set and maintain this internal clock have found that
the sugars produced by plants are key to timekeeping.
Plants produce sugar through photosynthesis. This is their way of converting the sun’s energy
into a usable chemical form needed for growth and function. These sugars also play a role in
The production of sugars was found to regulate key genes responsible for the 24-hour rhythm.
Sugar levels within a plant play a vital role in synchronizing circadian rhythms with its surrounding
environment. Inhibiting photosynthesis, for example, slowed the plants internal clock by between
2 and 3 hours.”
Plants continuously measure the amount of sugar in the cells and uses this information to make the
Plants use sugars to tell the time of day.
Photosynthesis has a profound effect on setting and maintaining robust circadian rhythms,
demonstrating a critical role for metabolism in regulation of the circadian clock. The accumulation
of sugar within the plant provides a kind of feedback for the circadian cycle in plants – a bit like
resetting a stopwatch. This might be a way of telling the plant that energy in the form of sugars
is available to perform important metabolic tasks.