North Carolina State University News Services Box 7504 Raleigh, NC 27695 (919) 515-3470
Media Contacts: Dr. Eric Davies, 919/515-2727, or [email protected]
Tim Lucas, News Services, 919/515-3470, or [email protected]
June 3, 1997
Study Finds Electrical Signals Can Spark Gene Expression in Plants
FOR IMMEDIATE RELEASE
A new study coauthored by a North Carolina State University botanist shows for the first time that electrical signals can trigger rapid gene expression in plants.
The study, published this month (June 1997) in the European science journal Planta, shows when an electric stimulus is used to wound a tomato leaf, bioelectrical signals are rapidly transmitted from the injured cells to other cells throughout the plant. These signals, known as action potentials, alert the cells to increase their production of naturally occurring chemicals called proteinase inhibitors (pin), which boost the plant's resistance to insect feeding.
Scientists have long known that plants possess such a defense mechanism -- it was first reported in the scientific press more than 20 years ago -- but until recently, most plant physiologists believed the intercellular warning signals were chemical in nature.
"Proving that a genuine electrical signal can turn on genes is important because it raises the possibility that we may be able to use electrical stimulation as an environmentally sound means for increasing crop resistance to pests," says Dr. Eric Davies, professor and head of NC State's Department of Botany.
In repeated experiments, Davies and coauthor Dr. Bratislav Stankovic of Ohio State University found that pin levels rose three- to five-fold throughout the plant within 15 minutes of an electrical stimulation, and up to 15-fold within a hour. Levels began to revert within two hours.
The researchers found wounding a leaf with a low flame also could spur large, rapid increases in temporary pin production, but due to a different signalling mechanism. The sudden loss of hydraulic tension in the dead tissue of the burned cells causes a plantwide hydraulic pressure surge which triggers an electrical reaction -- called a variation potential -- in adjacent living cells. Unlike action potentials, which spur uniform pin production plantwide, variation potentials were found to promote varying levels of pin production, with the highest levels occurring in cells nearest the wound.
Davies and Stankovic also found that variation potentials may spur systemic expression of calmodulin, a gene that plays a key role in initiating many information processes in plants, including their responses to cold and heat, gravity and touch.
To rule out the possibility the signals were chemical in nature, researchers attached a cooling ring to leaf petioles prior to wounding them. This prevented the leaves from transmitting chemicals out through their phloem, or vascular system. As further proof, Davies and Stankovic analyzed the electrical signals transmitted from the wounded leaf. "We found that if you cut the leaf off before the electrical signal was transmitted, there was no change in gene expression outside the wounded leaf itself. But if we cut it off after the transmission of the signal it made no difference. Gene expression throughout the plant was neither stopped nor reduced," Davies says.
Although there have been other studies in recent years that have offered evidence that nonchemical signals play a role in gene expression, Davies and Stankovic's work is the first to distinguish conclusively which types of nonchemical signals at are work, and the speed and extent to which the signals are transmitted throughout the plant.
Their research was funded by grants from the National Science Foundation, the University of Nebraska-Lincoln (UNL) Research Council and the UNL Center for Biotechnology. Davies formerly was a faculty member at UNL, and Stankovic was his graduate student there.
Further testing to evaluate the feasibility and effectiveness of electrically stimulated gene expression will be needed before farmers or crop breeders could put it into practice, Davies says. A more immediate benefit of his work is that it expands scientists' understanding of the fundamental intercellular communication processes used by plants.
"By proving that both electrical and hydraulic signals can trigger gene-specific expression, we show that plants are a bit more complex than we once thought. They can distinguish between various environmental stimuli and respond with the most appropriate type of intercellular signalling mechanism -- be it chemical, electrical, hydraulic or a combination thereof," he says.
That's information breeders, genetic engineers and other plant scientists need to take into account when conducting future research, Davies says. "We need to broaden the scope of our investigations and give these so-called ëlower life forms' a bit more respect. It's only when we recognize and understand the full range of sophisticated intercellular communication processes employed by plants that we will best understand how to manipulate and modify them."
-- lucas --
NOTE TO EDITORS: An abstract of Davies and Stankovic's paper follows. For a copy of the full paper, contact Tim Lucas at (919) 515-3470, or [email protected]
Intercellular Communication in Plants: Electrical Stimulation of Proteinase Inhibitor Gene
Expression in Tomato
By B. Stankovic, Ohio State University, and E. Davies, North Carolina State University
Published June 1997 in Planta
ABSTRACT: Tomato (Lycopersicon esculentum L.) plants accumulate proteinase inhibitor (pin) mRNA in response to various stimuli in leaves distant from those treated. Most earlier work suggests that the intercellular wound signals are chemical; we have tried to determine whether electrical or hydraulic signals can also evoke systemic pin expression. We used a mild flame to evoke a hydraulic signal and its local electrical aftermath, the variation potential (VP), and an electric stimulus to trigger an action potential (AP). Under medium light, wounding evoked a 3- to 5-fold systemic increase in pin mRNA within 15 min., suggesting involvement of a rapidly transmitted signal. Wounding also triggered a transient systemic increase in calmodulin (cal) mRNA under medium light conditions. Wounded plants exhibited electrical responses (VP) and yielded 5- to 15-fold increases in pin mRNA within 1 hr. Electrically stimulated plants that transmitted an AP to the analyzed leaf exhibited similarly lar
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