Biology Reference
In-Depth Information
Plants generate electric signals in response to many environmental stimuli and
stresses, such as extreme temperatures, diseases, and attacks by animals, and have
evolved relevant defense mechanisms. These electrical signals are propagated locally
or globally in the plant tissues and organs.
In response to damage caused by a caterpillar, a tomato leaf induces an action
potential and propagates it to other leaves, which leads to synthesis in all of them
of a substance that is toxic to the attacker. It is also believed that jasmonic acid (JA)
produced in the wounded leaf may travel throughout the plant body ( Sato et al.,
2011 ) and trigger production of the toxic substance by all the leaves. However, the
rapidity of the response by distant leaves contradicted evidence of the involvement
of chemicals in the defense response. This, as well as the fact that electrical stimula-
tion alone can induce the same response, demonstrates that the response results from
the propagation of the action potential induced by the caterpillar attack ( Leys et al.,
1999; Stankovi´ and Davies, 1997; Wildon et al., 1992 ). The action potential induced
by the caterpillar attack travels to other leaves.
There is evidence that electric signals are involved in the regulation of growth,
respiration and water uptake, and photosynthesis in plants ( Koziolek et al., 2003 ).
Besides the role of action potentials and variation potentials, a new type of long-
distance propagation that is transmitted systemically but varies in intensity from leaf
to leaf that is defined as systemic potential (SP) has been recently demonstrated in
plants and can be induced chemically or by cutting ( Zimmermann et al., 2009 ).
There are two modes of the propagation of action potentials in plants. In lower
plants and other plants such as Dionaea flytraps, they propagate in all directions,
whereas in higher plants, they propagate along the plant axis via vascular bundles
(xylem) that are used for water and nutrient transport ( Brenner et al., 2006 ). The
Venus flytrap, Dionaea muscipula , offers a curious example that illustrates the role
of propagation of action potentials in determining plant behavior. At the apex of
leaves, this plant has two half-open lobes that it uses as traps to catch insects, which
are digested and used as food. Entrance of an insect into the inner surface of lobes
is perceived by mechanosensory hairs as a stimulus and induces an action potential,
which, via plasmodesmata (small channels connecting plant cells to each other), is
conducted to all lobe cells, thus stimulating the motor cells of the midrib to close the
lobes and trap the insect in less than a second ( Figure 1.29 ).
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