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A record-breaking pollen catapult. Nature 435:164

Authors:

Abstract

The release of stored elastic energy often drives rapid movements in animal systems1, 2, and plant components employing this mechanism should be able to move with similar speed. Here we describe how the flower stamens of the bunchberry dogwood (Cornus canadensis) rely on this principle to catapult pollen into the air as the flower opens explosively3, 4, 5. Our high-speed video observations show that the flower opens in less than 0.5 ms — to our knowledge, the fastest movement so far recorded in a plant.
8. Efstathios, M., Marcus, D., Desnoyer, M. & Lipson, H. Designed
and Evolved Blueprints For Physical Self-Replicating Machines in
Proc. Ninth Int. Conf. Artificial Life 15–20 (Boston,
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2004 2661–2666 (Sendai, Japan, 2004).
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Mechatron. 7, 462–472 (2002).
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Vol. 2801 (eds Banzhaf, W. et al.) 1–9 (Springer, Germany, 2003).
Supplementary information accompanies this communication on
Nature’s website.
Competing financial interests: declared none.
Botany
A record-breaking
pollen catapult
T
he release of stored elastic energy often
drives rapid movements in animal sys-
tems
1,2
, and plant components employ-
ing this mechanism should be able to move
with similar speed. Here we describe how
the flower stamens of the bunchberry dog-
wood (Cornus canadensis) rely on this prin-
ciple to catapult pollen into the air as the
flower opens explosively
3–5
. Our high-speed
video observations show that the flower
opens in less than 0.5 ms — to our knowl-
edge, the fastest movement so far recorded
in a plant.
Cornus canadensis grows in dense carpets
in the vast spruce-fir forests of the North
American taiga.As bunchberry flowers burst
open, their petals rapidly separate and flip
back to release the stamens (Fig. 1). During
the first 0.3 ms,the stamens accelerate at up to
24,0006,000 m s
2
(2,400g), reaching the
high speed (3.10.5ms
1
) necessary to
propel pollen, which is light and rapidly
decelerated by air resistance (terminal velocity,
0.120.03ms
1
(means.e.m.);n7).The
pollen granules are launched to an impressive
height of 2.5 cm (range, 2.2–2.7 cm; n5),
which is more than ten times the height of
the flower: from this height, they can be car-
ried away by the wind. (For methods and
movies, see supplementary information.)
Petals open independently of stamen
activity, moving out of their way within the
first 0.2 ms (Fig. 1).Petals attain a maximum
speed of 6.70.5ms
1
, accelerating at up
to 22,0006,000 m s
2
(or 2,200g). The
process of petal opening and pollen launch
in bunchberry plants occurs faster than the
opening of Impatiens pallida fruits
(2.8–5.8 ms, n3, see supplementary infor-
mation); the snap of venus flytraps (Dionaea
muscipula; 100 ms)
6
; the leap of froghoppers
(Philaenus spumarius; 0.5–1.0 ms)
1
; or the
strike of the mantis shrimp (Odontodactylus
scyllarus; 2.7ms)
2
.
As in these other organisms
1,2,6
, rapid
movements in bunchberry flowers rely on
stored mechanical energy. Physiological
processes, which take about a millisecond
for each enzymatic reaction
7
, are not
required for the explosion itself.We find that
the flowers will open even when the stamen
filaments have been crippled by treatment
with sodium azide. But the flowers do not
open if their turgor is reduced: dehydration
of flowers with sucrose decreases the extent
of opening, although subsequent rehydra-
tion allows them to open fully (results not
shown). Turgor pressure is therefore
required in the production of mechanical
energy for explosive flower opening.
Bunchberry stamens are designed like
miniature medieval trebuchets — specialized
catapults that maximize throwing distance
by having the payload (pollen in the anther)
attached to the throwing arm (filament) by a
hinge or flexible strap (thin vascular strand
connecting the anther to the filament tip).
This floral trebuchet enables stamens to pro-
pel pollen upwards faster than would a simple
catapult. After the petals open, the bent fila-
ments unfold,releasing elastic energy. The tip
of the filament follows an arc,but the rotation
of the anther about the filament tip allows it
to accelerate pollen upwards to its maximum
vertical speed, and the pollen is released only
as it starts to accelerate horizontally (Fig.2).
The rapid opening of the self-incom-
patible
8
bunchberry may enhance cross-
pollination in two ways. First, when insects
trigger flower opening, the pollen released
sticks to their body hairs until it is transferred
to an adhesive stigma. The force required to
open flowers (0.1–0.5 mN) favours large
pollinators (bumblebees, for example) that
move rapidly between inflorescences; it effec-
tively excludes smaller, less mobile visitors
such as ants.Second,pollen from flowers that
open by themselves may be carried by wind
currents. Indoors, pollen is transported over
22 cm (more than 100 times the size of the
flower) and outdoors, in the presence of a
steady wind, pollen can move farther than a
metre. Exploding flowers enhance insect
pollination and may allow wind pollination,
adding to growing evidence that flowers often
use multiple pollination mechanisms
9,10
.
Joan Edwards*, Dwight Whitaker†,
Sarah Klionsky*, Marta J. Laskowski‡
Departments of *Biology and Physics, Williams
College, Williamstown, Massachusetts 01267, USA
e-mail: joan.edwards@williams.edu
Biology Department, Oberlin College, Oberlin,
Ohio 44074, USA
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(2004).
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4. Marie-Victorin, F. Flore Laurentienne (Imprimerie de la Salle,
Montreal, 1935).
5. Mosquin, T. Can. Field-Nat. 99, 1–6 (1985).
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433, 421– 425 (2005)
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1995).
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(1987).
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Smith, D. C. Nature 384, 615 (1996).
10.Kearns, C. A., Inouye, D. W. & Waser, D. N. Annu.Rev.Ecol.Syst.
29, 83–112 (1998).
Supplementary information accompanies this communication on
Nature’s website.
Competing financial interests: declared none.
brief communications
164 NATURE
|
VOL 435
|
12 MAY 2005
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www.nature.com/nature
0 ms 0.2 ms 0.4 ms 1.0 ms
Figure 1 Bunchberry flower opening, recorded on video at 10,000 frames per second. Time elapsed is indicated. First frame shows a
closed flower with four petals fused at the tip, restraining the stamens. Blur represents the distance moved in 0.1 ms. Scale bar, 1mm.
Figure 2 Dynamics of floral explosion. a, Coordinates x and y of positions of the filament tip (blue triangles) and anther tip (red circles), plotted
at 0.1-ms intervals. Inset, a single stamen; points used to plot positions are indicated. Arrows, stamen positions just before pollen release.
b, Coordinates x and y of velocity components of the anther (top) and filament (bottom) as a function of time, derived from the first six points
in a. Arrows, velocity just before pollen release. Error bars represent uncertainty in measurements from a, propagated as random errors.
0.3
y
y
x
x
0.5
0.1
Time (ms)
1
2
3
1
2
3
b
Velocity (m s
–1
)
1.0
0.5
0.5 1.0 1.5
Position x (mm)
1.5
a
Position y (mm)
12.5 brief comms NS 5/5/05 5:47 PM Page 164
Nature
Publishing
Group
© 2005
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