Touch-Responsive Behaviors and Gene Expression in Plants - Communication in Plants: Neuronal Aspects of Plant Life - page 251

creatures that have ventured close to the bladder opening, the door bursts
open within 30 ms and water, and any unfortunate creatures caught in the
current, rushes the chamber as the outer walls flip from concave to slightly
convex in shape.
The touch-induced leaflet movements of the sensitive plant ( Mimosa
pudica ) are more likely to occur for protective rather than aggressive pur-
poses and adjacent, but untouched, leaflets fold up (Fig. 17.1d,e). If all the
leaflets of the compound leaf undergo this movement, as in response to
a strong mechanical stimulation such as wounding, the whole leaf nearly
disappears (Simons 1981; Malone 1994). Electrical, hydraulic and chemical
signals have all been implicated in carrying the long-range information that
enables responses even in unwounded leaves (Ricca 1916; Houwinck 1935;
Simons 1981; Fromm and Eschrich 1988; Malone 1994; Fleurat-Lessard et
al. 1997; Stahlberg and Cosgrove 1997).
17.2
Thigmotropism - Vines, Tendrils and Roots
Vines, tendrils and roots show expert thigmotropic behaviors. The Mon-
stera vine uses both darkness and touch as growth and differentiation
signals. The young vine searches the forest floor for darkness and grows
toward dark shadows, a behavior called skototropism, to reach the base
of its chosen host tree (Strong and Ray 1975). Upon touching the tree,
thevineturnstogrowupwardandundergoesmorphogeneticalterations
such as leaf development and expansion as it ascends (Strong and Ray
1975).
Tendril coiling also enables plants to reach sunlit heights that would
otherwise require the expensive generation and maintenance of a tall sup-
porting trunk. The touch-sensitive tip coiling behaviors of tendrils begin
within seconds to minutes; not as fast as the trapping responses described
before, but with a time frame that selectively enables winding around and
attachment to stable objects perceived in the local environment (Jaffe and
Galston 1968). Indeed, tendrils that respond to transient touch stimula-
tion are able to reverse their behavior by unwinding (Jaffe and Galston
1968). Tendrils are highly sensitive, being able to perceive stimuli of a few
milligrams or less (Darwin 1906; Simons 1992). In addition, tendrils are
capable of distinguishing potentially productive and nonproductive per-
turbations; tendrils fail to coil in response to water droplets (Jaffe and
Galston 1968). Tendrils can be thigmotropic, displaying coiling in a direc-
tion dependent upon the site of stimulation, or thigmonastic in that the
direction of the coiling is predetermined and the touch stimulation simply
triggers the response (Jaffe and Galston 1968). Octadecanoids and auxin