Agriculture Reference
In-Depth Information
17
Touch-Responsive Behaviors
and Gene Expression in Plants
Elizabeth McCormack, Luis Velasquez,
Nikkí A. Delk, Janet Braam
Abstract
The abilities of plants to perceive stimuli in their environment are often over-
looked. Yet hints of exquisite sensitivities abound. Indeed, although it is not generally
appreciated, probably all plants can perceive and respond to simple mechanostimulation
like touch. We will briefly review some of the more spectacular touch responses of special-
ized plants and then discuss developmental and molecular responses to touch that occur
in nonspecialized plants. Many of these data and concepts have recently been reviewed by
Braam (
New Phytol.
165:373-389, 2005).
17.1
Specialized Plants - Touch Responses That Catch Attention
Fast reactions are easy to see and therefore the touch responses of plants
like Venus' flytrap, sundew and
Mimosa
are well recognized. Venus' flytrap
(
Dionaea muscipula
) and sundew (e.g.,
Drosera rotundifolia
)usetouch-
sensitive responses to carry out carnivory by cleverly trapping insects;
these touch responses enable them to thrive in nitrogen poor soils. Venus'
flytrap awaits potential prey by spreading wide its specialized bi-lobed
leaves edged with needle-shaped tines (Fig. 17.1a). Trigger hairs on the
ventral leaf surface must be touch-stimulated multiple times to induce trap
closure (Curtis 1834). Recent examination of the changes that take place
in leaf geometry upon rapid closing reveal that the rapid closure comes
from a snap buckling of the leaves as they transition from open to closed
state (Forterre et al. 2005). The signaling that must occur between the trig-
ger hairs and the closure response is still somewhat mysterious; however,
intercellular electrical changes are detected and may act as intermediary
signals (Burdon-Sanderson 1873; Jacobs 1954; Jacobson 1965; Simons 1981;
Fagerberg and Allain 1991).
The sundew attracts insects with its glistening mucilage-laden tentacles
(Fig. 17.1b). Insects that alight upon the tentacle surfaces find themselves
bound by the gluey mucilage. The agitated movements of the insect attempt-
ing to loosen itself from the sticky surface lead to touch-induced tropic and
nastic movements of neighboring tentacles (Darwin 1893; Lloyd 1942).
An indentation of the leaf generates a cup-shaped enclosure (Fig. 17.1b)
where the meal is dissolved. The selective sensitivity of the tentacles is
remarkable. Darwin (1880, 1893) reported that the tentacles are capable of
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