Allergic to Rubber?
In her laboratory, plant physiologist Katrina Cornish checks seedlings produced
for use in experiments to improve guayule plants. The experimental,
allergen-free latex products shown were made from guayule.
Scientists Probe Potential of Guayule Latex
Rubber from a native southwestern shrub called guayule (pronounced
why-YOU-lee) may become a new source of high-quality, hypoallergenic latex for
medical, industrial, and home products.
Scientists with the Agricultural Research
Service at Albany, California, were the first to discover that the milky
latex from this hardy plant is free of allergens that can cause severe
reactions, such as anaphylactic shock or even death.
"An estimated 20 million Americans," says plant physiologist
Katrina Cornish, "are allergic to the latex in gloves, catheters, condoms,
or other products made from the most widely used source, the Brazilian rubber
Cornish, with ARS at Albany, and agency colleagues in Phoenix, Arizona,
explore new ways to make production of guayule latex practical, efficient, and
profitable. The ARS experimentssome in cooperation with universities in
California, Arizona, New Mexico, Texas, and Utahaddress conventional
breeding and genetic engineering of the plant, as well as its planting,
cultivation, and harvesting. Other studies investigate techniques for
extracting, storing, and processing the latex.
Composed of rubber particles in a water-based suspension, latex is a higher
value product than solid rubber. This fact, plus the urgent need for
hypoallergenic alternatives to conventional latex, has made guayule's
latexas opposed to its solid rubberthe focus of the ARS research.
Until this decade, most studies of guayule, Parthenium argentatum,
dealt primarily with its rubber, which hasn't been produced commercially in
this country since 1929.
Today's guayule plants are superior to those of the past, thanks to plant
breeding by ARS and university scientists in Arizona. In 1997, these
researchers offered growers seed from guayule plants selected for fast growth
and high latex content.
ARS geneticists Terry A. Coffelt and David A. Dierig, who are at the U.S.
Water Conservation Laboratory in Phoenix, are continuing the quest for even
better guayule. They are screening thousands of candidate plants in greenhouses
and outdoor plots. Their experiments also help breeders pinpoint whether
environment or genetics is the dominant factor affecting growth rates and latex
Biotech experiments by Cornish focus on genetically engineering guayule
plants to boost their latex levels. "Guayule lines that we've
tested," says Cornish, "contain up to 10 percent latex. Even a small
increase in that latex level could mean a significant increase in potential
profits for growers and processors."
Cornish, along with Christopher J.D. Mau and Mary H. Chapman at the Western
Regional Research Center in Albany, and former Albany researcher Javier
Castillón, developed a faster, easier way to move new genes into guayule
tissue in the lab.
Their procedure, patterned after one used by scientists elsewhere with other
plant species, relies on bathing pieces of leaves in a solution containing a
reworked form of a microbe, Agrobacterium tumefaciens. The modified
bacterium has the experimental genes inside and can slip them into guayule
cells. The leaf pieces are nurtured to form shoots and, later, roots.
The team is apparently the first to use this approach successfully with
Says Mau, "With this technique, we get more genetically engineered
guayule plants than with an earlier, more cumbersome procedure. That other
approach required piercing plants with a very thin needle to make an entryway
for the microbe."
Castillón and Cornish also produced a new, simplified procedure for
successfully raising identical copiesor clonesof promising plants,
using shoots snipped from the parent plant. They cultivate shoots in small
containers filled with a nutrient-rich liquid and plugssmall, stubby
rolls of a papery material that look something like miniature, tightly
compressed rolls of paper towels. Later, they move the developing plantlet,
with new roots anchoring it to the plug, directly into greenhouse pots.
This procedure, not yet reported by any other guayule researchers, causes
little if any damage to guayule's young, fragile roots. An earlier technique
was riskier: A plantlet had to be pried from a test tube and nutrient gel
pulled from its roots before it could be transplanted to pots.
Plantlets raised with the Albany technique form roots as readily as those
grown with the earlier procedure. And they adjust to the greenhouse in a few
days instead of several weeks. Used successfully at Albany for more than 3
years, the new procedure has been adopted by a lab in South Africa. It is
expected to be in use in a guayule display planned for next year at Disney's
Epcot Center in Florida.
Estimating What You've Got
Plant physiologist Katrina Cornish and associate Christopher Mau examine
guayule plantlets that they have genetically engineered.
ARS scientists Francis S. Nakayama and Stephen H. Vinyard in Phoenix
collaborated with Cornish, Chapman, and statistician Linda C. Whitehand at
Albany to develop a simple, reliable procedure for estimating latex levels in
The basic approach requires cutting branches into half-inch-long pieces,
grinding them for precise periods in a blender, and filtering the resulting
liquid, or homogenate. The liquid is spun in a device called a microcentrifuge
to separate the creamy latex from the rest of the slurry. Then the latex is
coagulated, dried, and measured.
"We estimate," says Nakayama, "that we're extracting at least
90 percent of the latex in each specimen without having to use harsh
The researchers anticipate that it won't be practical for latex producers to
always process guayule shrubs immediately after harvest. Earlier studies
already showed that guayule rubber levels decrease in storage, but the Albany
and Phoenix scientists were the first to track changes in latex levels from
both stored shrubs and stored homogenate.
Medium-size branchesthose about one-fourth- to one-half-inch in
diameterconsistently had more extractable latex than smaller or larger
branches tested throughout a 5-week period. Stored branches retained all of
their latex for 2 weeks. But homogenates didn't begin to lose latex until the
beginning of the fifth week, "meaning that homogenate is the best option
for processors who need to store the harvest for more than 2 weeks," says
"Up until that time," says Nakayama, "it is probably cheaper
to store the crop as whole shrubs, provided they are not allowed to dry out.
Further studies will give us more details about the cost advantages of the two
storage options."By Marcia
Wood, Agricultural Research Service Information Staff.
This research is part of New Uses, Quality, and Marketability of Plant
Products, an ARS National Program described on the World Wide Web at
Katrina Cornish is in the
USDA-ARS Crop Improvement and Utilization
Research Unit, Western Regional Research Center, 800 Buchanan St., Albany,
CA 94710; phone (510) 559-5950, fax (510) 559-5777.
Francis S. Nakayama is
in the USDA-ARS
Environmental and Plant Dynamics Research Unit, U.S. Water Conservation
Laboratory, 4331 E. Broadway Rd., Phoenix, AZ 85040; phone (602) 379-4356,
ext. 255, fax (602) 379-4355.
"Allergic to Rubber?" was published in the
May 1999 issue of Agricultural