don't have nervous systems or immune systems.
But they do have their own type of cellular
communication systems through lipid signals, says Kent Chapman.
Chapman, University of North Texas associate
professor of biological sciences, and Swati Tripathy, postdoctoral research
associate, are the first researchers to show that some lipid compounds
act as signaling molecules in plants that encounter pathogens or other
elements that cause stress to their cells and lead to cell death. These
lipids appear to block enzymes that contribute to cellular collapse and
This finding in basic cellular research could have many applications
from delaying the ripening of fresh fruits
to preserving the freshness of cut flowers.
Chapman compares these signaling lipids,
which are derived from N-acylphosphatianolamine (NAPE), a cellular membrane
component in all multicellular organisms, to the signaling lipids in human
"Unlike humans, plants don't have circulating
antibodies, and they can't go inside to avoid stress from hot and cold
weather. They can't put on sunscreen to avoid stress from UV rays," he
says. "They really have to be much more sophisticated in responding to
their environments than we do."
stress defense for plants
Chapman has studied
plant lipid biochemistry since he became a UNT faculty member in 1993.
He was attracted to the unusual chemical structure of NAPE
three fatty acids instead of the usual two
found in typical membrane lipids.
In addition, Chapman's UNT research team
had found the lipid at higher concentrations in seeds than in any other
parts of a plant.
"Seeds are only 10 percent water, and there
isn't any cellular stress that is worse than dehydration," he says. "It's
not proven, but we may see an accumulation of these lipids in seeds as
a result of dehydration stress."
In 1995, Chapman and Tripathy began to
experiment with NAPE as a defense signal in tobacco plants. They introduced
pure proteins from pathogens into the plants' leaves, believing the proteins
would activate the same defense response that bacteria or other pathogens
"We chose to use protein because if you
use bacteria, you have to deal with the bacteria's own lipids," Chapman
says. "The proteins did activate the metabolism of NAPE."
In additional experiments, release of the
lipid activated the plants' own defense systems.
the life of cut flowers
Chapman and researcher
Shea Austin-Brown next searched for other biological functions for this
obscure class of lipids. They found that these lipids inhibit a type of
These enzymes are normally activated in
plants during tissue collapse, which occurs in flowers when they are cut
from their stems. Chapman wondered whether lipid supplements could delay
the degradation and tissue death in cut flowers and other plant systems.
He and Austin-Brown soaked the cut flower stems in a solution of synthetic
lipids and compared them to flowers soaked in water or solutions commonly
used by florists.
Degrading cells in cut flowers lead to
droopy blossoms and stems after a few days. However, these plant lipids
seem to inhibit the enzymes that participate in that process, resulting
in full and fresh blossoms and rigid stems for a longer period of time,
"We measured the diameters of the blossoms
before soaking in the solution, then measured them again days later to
note cell degradation," he says. "The blossom measurements varied depending
on the quality of the flower and whether the correct dosage was soaked
up. But generally, the flowers in our solution were far superior to others.
This process is almost like putting a protectant into the flower."
Chapman experimented with carnations, roses,
daisies and wildflowers, all with the same results.
"We also tested the concentration range.
Higher concentrations of our solution extend the life of flowers for a
longer time while they are in a vase," he says.
UNT has applied for a patent for the method
of using these solutions to preserve cut flowers. Chapman says the method
could revolutionize the cut flower industry
a $7 billion industry in the United States alone.
"If only a small percentage of those handling
flowers treated them in the solution, it would lead to a significant savings
in terms of shipping, inventory costs and customer satisfaction," he says.
"When you buy cut flowers, you want them to last for a while. But right
now, some flowers last only 24 to 48 hours before wilting." Flowers in
Chapman's experiments were still fresh after 17 days.
He adds that the UNT-developed solution
could replace a silver compound solution florists have used to preserve
flowers. That solution, he says, is heavily regulated by the Environmental
Protection Agency because of concerns about heavy metal pollution in wastewater.
In addition to
cut flowers, the freshness of fruits and vegetables might be preserved
with variations of the lipid formulas, Chapman says.
"Tomatoes, for example, taste the best
when they ripen on the vine," he says. "But if you let them ripen on the
vine and then cut them for shipping to grocery stores, the cellular degradation
process begins and the tomatoes start getting too ripe and soft. Dosing
them could be a good way to temporarily delay further ripening after they're
Chapman and his research team plan to continue
to investigate whether lipid signaling is involved in different types
of environmental stress.
"NAPE metabolism may be the central mechanism
activated in response to temperature stress," he says. "If we can manipulate
the levels of NAPE metabolites in response to different environmental
stress, we could successfully grow plants in climates that are warmer
or cooler than normal."
Part of Chapman's research on NAPE will
be published in a special issue of the journal Chemistry
and Physics of Lipids later this year. He notes that scientists
had long believed that NAPE had no real function in any organism.
"We found out not only is that false, but
the lipid participates in a vast array of biological functions," he says.
"Science is meant to be skeptical, but there's really nothing in an organism
that is there by accident."