Transcript Plants Keep Track of the Hours and the Seasons

Plants Keep Track of the Hours
and the Seasons
Remember the tropical plant Mimosa pudica
that quickly folds up when touched
(thigmotropism)? Well, every day at dawn, it
unfolds its leaves and every day at dusk it folds
its leaves. These movements, seen in many
other plants as well, form a regular daily
pattern.
Vocabulary
circadian rhythm:
rhythmic pattern of
behavior (in an
animal) or biological
cycle (in a plant) that
follows an
approximately 24hour natural cycle
• You respond to changes in
time……
• Your pulse rate, blood
pressure, and body
temperature change with the
time of day
• Different time zones could
affect you—what we call jet
lag.
• An organism's "biological
clock" is set by daily signals
from the environment,
especially light.
Day Length and Seasons
In addition to maintaining a 24-hour cycle, plants
also respond to changes in environmental cues
that come with the seasons.
Some plants flower in the spring, for instance,
while others flower in the fall.
i.e. Tulips (spring) and Christmas cactus (fall)
Pictures
Christmas Cactus
Blooms in the fall usually close to Christmas hence
the name…..
flower in fall or winter when the dark period
exceeds a certain length, called critical night length
Vocabulary
photoperiodism: plant
response to cycles of light
and darkness
short-day plant: plant that
blooms when the dark
period exceeds a critical
length
long-day plant: plant that
blooms when the dark
period is shorter than a
critical length
day-neutral plant: plant that
blooms when it reaches a
certain stage of maturity,
regardless of day length
How do we use this information
in real life….
Flower growers use information about
photoperiodism to produce certain flowers out of
season.
Chrysanthemums, for instance, are short-day
plants that normally bloom in autumn. But a
florist can prevent a chrysanthemum from
blooming until the spring by exposing the plants
to flashes of light during the long autumn and
winter nights. The plant thus detects two short
nights, instead of one long night, and fails to
bloom.
Chrysanthemums
How does a plant monitor day
length as the seasons change?
•Sunrise and sunset are detected by pigmented
proteins called phytochromes
•phytochromes absorb the red light that is
abundant at sunrise, they change shape to an
active form that triggers a variety of plant
responses.
•After sunset, the phytochromes gradually
change back to their inactive form