Pop off most dandelion heads and, just for a second, white sap oozes freely from the wound.
Pop the head off a new genetically engineered dandelion, however, and white sap oozes for minutes, allowing scientists to gather five times more latex than from the average dandelion.
The research could lead to a variety of new or cheaper products, including new car tires or even new pharmaceutical drugs.
"We have identified the enzyme responsible for the rapid polymerization and have switched it off," explained Dirk Prufer, a scientist at Fraunhofer Institute in Munich, Germany, who is developing the technology.
"If the plants were to be cultivated on a large scale, every hectare would produce 500 to 1,000 kilograms (1,100 to 2,200 pounds) of latex per growing season."
For thousands of years, most of the world's rubber has come from tropical rubber trees. A diagonal cut in the trunk allows the white latex to drip into hanging cans, which can then be harvested and eventually turned into a variety of different materials.
Natural rubber contains trace amounts of biological impurities, however. For car tire makers, those impurities give vulcanized rubber a give and elasticity they can't get anywhere else. For some hospital workers, however, those same impurities can trigger life-threatening allergic reactions.
Synthetic or petroleum-based rubber typically has fewer impurities than natural rubber which makes it ideal for applications like allergy-free gloves.
Dandelion-derived latex has both the elasticity of natural rubber but lacks the allergens, making it an ideal alternative to rubber tree latex.
Unfortunately, dandelion-derived latex is also difficult to obtain.
Because dandelion latex transforms from a liquid to a solid on contact with the air (known as polymerization), turpentine and naphtha are usually required to chemically extract the latex from the shredded remains of Russian dandelions.
To eliminate polyphenol oxidase, the enzyme responsible for the phase change, the German scientists engineered a special virus. Once inside, the virus deleted the offending genetic sequence from the Russian dandelion's DNA. Pop the head off an infected dandelion, and the latex begins to flow freely.
Eliminating polymerization means dandelion latex can be harvested using a low-speed centrifuge, a much easier and cheaper alternative than chemical solvents. It also means up to five times the amount of rubber can be harvested than with chemical extraction.
Allergy-free latex is only one potential use for dandelion-derived latex. If the gene that eliminates polymerization can be knocked out, genes that produce other enzymes can be added using the same method.
Among the enzymes that researchers could add include insulin for diabetics, artificial sugars and pharmaceutical drugs for other diseases.
Adding genes is more controversial than removing genes, however. Using viral vectors ensures that virtually any attempt to plant harvestable amounts of transgenic dandelions will come up against fierce resistance from groups opposed to genetically modified crops. Which is why the Germans next attempt is to try and breed the offending dandelion gene using traditional breeding methods.
"We did it for a gene in the potato," said Prufer. "It took us about five years though."
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William Ravlin, a scientist at Ohio State University who also works on dandelion-derived rubber, thinks five years is too long. Genetic modification of plants is a pariah in Europe, but Americans tend to have a more liberal attitude toward GM, especially when it comes to plants that don't produce food.
The elimination of polyphenol oxidase "sounds like a very good discovery," said Ravlin. "Genetic modification of dandelions will probably speed up the number of potential applications, but it's not completely necessary either."
Ravlin's own research, in association with tire maker Bridgestone and with a grant from the state of Ohio, has focused on finding strains of dandelions that produce larger amounts of rubber in latex, a work he describes as "incremental."
If economically feasible, the work of both Ravlin and Prufer could quickly become exponential.
"If, say, one dandelion has 100 seeds (and they usually have many more than that), you now have 100 plants, which are now producing 100 seeds each," said Ravlin. "You can see how rapidly that could ramp up production. But first you have to get to that first plant, and that will take a lot of effort."