Pulvinus
A pulvinus is a localized swelling
at a joint (usually in a leaf or
stem) that causes the organ to
move (fold or unfold).
This basic type of reversable
movement is called a nastic
movement.
Types include:
Nyctinastic – movement
related to day/night cycles
Thigmonastic - movement
caused by touch
Samnea leaves
unfolding as the
day begins.
Thermonastic – movement
related to temperature
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Pulvinus
Nyctinastic or sleep leaf movement in Oxalis.
Leaves fold around the petiole during the night (dark period) and unfold again in
the morning (light period). This patterned movement is called a Circadian rhythm.
Night
Day
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Pulvinus
Nyctinastic or sleep leaf movement in Oxalis.
Circadian leaf opening
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Pulvinus
Nyctinastic or sleep leaf movement in Oxalis.
The leaflet movement is
controlled by an area between
the leaflet and the petiole
called the pulvinus containing
motor cells.
Pulvinus
The pulvinus has a central
vascular core and an outer
cylinder of parenchyma motor
cells that shrink or swell based
on the cells turgor pressure.
Oxalis
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Pulvinus
Prayer plant (Maranta) also displays nyctinastic leaf movements.
It gets is common name from its daily, repetitive leaf folding and unfolding.
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Pulvinus
The area of the pulvinus appears wrinkled
to accommodate the folding and unfolding
as cells swell or loose turgor.
Pulvinus
folded
Pulvinus unfolded
Swisscheese plant (Monstera deliciosa)
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Pulvinus
The best known example of a thigmonastic movement occurs in the sensitive
plant (Mimosa pudica). Touching the leaf apparently stimulates an electrical
signal that changes the turgor in the pulvini of the leaflets and petiole
causing the leaflets to fold and the leaves to droop.
Leaves unfolded
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Leaves folded after being touched
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Pulvinus
Thigmonastic movement in sensitive plant (Mimosa pudica)
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Pulvinus
Another example of a thigmonastic movement can be seen in stamen
movement often termed stamen irritability. The stamens react to the
touch of a pollinator to abruptly move toward the visiting insect and
release pollen. The best documented example is in barberry (Berberis).
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Pulvinus
A progression of stamen
closure as each stamen
is touched. The closure
movement is rapid, but
the stamens will
gradually move back into
an open position after
about 5 minutes.
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Pulvinus
Thigmonastic movement in barberry stamens.
The initial stamen
movement is in real
time, while the slower
stamen movement back
towards the petals has
been accelerated. Its
actual time is about 4
minutes.
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Pulvinus
An example of thermonasty can be seen in some early spring flowering plants
that open and close petals in response to temperature.
The usual pattern is for cold night temperatures to cause the petals to close
and as the day begins and temperatures increase, the petals gradually open.
Closed
Fully open
Opening
A cycle of opening and closing of the petals in bloodroot (Sanguinaria).
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Pulvinus
The most documented thermonastic petal movement can be seen in tulips.
Temperatures below about 50oF (4oC) cause petals to close.
The movement is reversible based on petal temperature.
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