New Application Ideas - Electro-Horticulture - page 110

• Different sets of genes can be activated based on signal transduction, triggered
from the plant's immune system when under attack.
• EmittedVOCscanrepelharmfulinsectswhilesimultaneouslyattractingpredatory
insects.
• Interactions with neighboring plants may elicit others to emit complementary
compounds to help fend off an attack.
It may have to do with the rate at which a cocktail of volatile aromatic compounds
are exuded from the plant's leaves and flowers. Some plants have natural self-defense
capabilities against insects or parasites, so under electrical stimulation, these effects may
be accentuated. Dr. Eric Davies, professor and head of North Carolina State University's
Department of Biology says that during experiments performed on tomato plants, he noted
thatelectricalsignals(APs)frominjuredcellscantriggerrapidgeneexpressionthatleadto
anincreaseintheproductionofproteinaseinhibitors.AlsoknownasPINs,thesechemicals
are known for increasing the plant's resistance to insect feeding damage. 4
The mechanisms behind this are multifold. Because of the plant's increased metabolism,
these compounds are stimulated into overproduction. Next, based on the increased
respiration, greater amounts of compounds can be exhaled into the nearby atmosphere.
The effect is further amplified through inter-plant communication messages which may
cause nearby plants to exude these substances as well 5 , creating a 'crowd-sourced' defense
mechanism.
In addition to creating volatile chemicals that may repel certain insects, these compounds
have also been used to attract parasitic insects that feed upon attackers 6 . An example of a
predator attractant behavior is this: when certain genes in potato plants are activated, they
cause the release of chemicals which make them attractive to predatory mites 7 .
Thisprocessisn'twithoutrisks.Whileplantscanemitsubstancestoxicforinsectattackers,
too much can prove harmful for the plant. Even though the toxic chemicals are generated
within the plant, if inhaled, it can cause stress. A negative factor in addition to the risk of
self-poisoning is the production cost of these compounds. Since plants typically consume
greateramountsofenergywhenunderattack,prolongedchemicalgenerationcanadversely
affectsystemsthatrequiregreatamountsofenergy,likereproductivefunctions,whichmay
affectfruitproduction.Whileitmaybepossibleforthestresstobeminimizedfromgreater
nutrient intake, in the long run it depends on the plant species, the length of time of the
attack, the insect's resistance to the counter-attack, and other factors.