Vile weed no longer

Dandelions, arguably the most annoying plant any gardener will come across (second only to stinging nettle). They are like the mosquitoes of the plant world. Except for those few people who use them in salads and wines, and that neighbour down the street who insists they’re his favourite flower, we’d all pretty much rather be rid of them. Perhaps we judge them too quickly; research is currently being done on the potential use of this prolific and unstoppable plant as a natural source for rubber production.

Rubber is a terpenoid compound, which today is produced in two different ways: synthetically or naturally. Natural rubber comes from the latex (milky fluid which exudes when the bark is cut) of the rubber tree (Hevea brasiliensis). Natural rubber has been used by humans for centuries, with the native peoples of central and South America being the first. Christopher Columbus even observed the use of a rubber ball during a native game known as Tlachtli. Natural rubber is still obtained from the rubber tree to this day.

Most natural rubber is harvested from plantations in Southeast Asia, with Thailand producing the most. Rubber trees seven years or older have a series of cuts made into their bark from which latex will then flow to be collected in a cup. Latex will flow for about one to three hours before the vesicles coagulate and it stops. Two or three days later the tree may be tapped again. Each tapping may yield around a half a cup of latex.

Synthetic rubber, on the other hand, is made by humans, being produced from the by-products of petroleum refinement, such as butadiene and styrene. Currently 70 per cent of all rubber used is synthetic. Synthetic rubber surpassed natural rubber usage because of war-time necessity related to restricted natural supply form Asia during the Second World War. Its dominance has continued because of the cheap price of oil following the war. However, with oil continually increasing in price it only makes sense to seek an alternative. According to the Rubber Manufacturers Association, it takes approximately seven gallons of oil to produce one tire — five gallons provide the actual materials, and two gallons provide the energy. Synthetic rubber also faces the challenge that it is simply not as good as natural rubber; whereas the rubber tree produces its latex using enzymes which yield a very regular structure, synthetic rubber produced by chemical reactions simply cannot attain the same quality. The greater resilience and strength of natural rubber is the reason why airplane tires are 80 per cent natural rubber, while car tires are only 20 per cent.

The limitation of using natural rubber is that it is still obtained by plantation farming. This practice is expensive and the trees take years to grow. Additionally, expanding plantation space in the tropics would likely involve cutting down areas of rainforest, which is generally a bad thing. So the search for an economically viable source of natural rubber to supplement the rubber tree holds a big reward if successful. To that end, two research teams have begun work on helping a species of dandelion fill that void.

Taraxacum kok-saghyz (TKS) or the Russian dandelion, is a weed that produces natural rubber in its latex. Although TKS is a small plant, its quick and robust growth could make it possible to yield two harvests a year, thus compensating for its size, and it could grow in areas of the world in which natural rubber production is not currently possible (i.e., places other than the rainforest). In one of the projects working with TKS Matthew Kleinhenz of Ohio State University has begun a breeding program to try and increase the rubber yield from the plant itself. Using good old-fashioned selection, Kleinhenz is grinding up the roots of the plants to extract the sap. After determining which plants have the highest rubber content he cross breeds them. The goal of the project is to create a line of plants that have a high rubber content and large enough roots to be harvested by machines similar to those used currently to harvest carrots.

The second group working on TKS is lead by Christian Schulze Gronover of the Fraunhofer Institute for Molecular Biology in Aachen, Germany. Using more sophisticated molecular techniques the team has identified the genes which TKS uses to produce rubber. Of particular interest is the gene for the enzyme polyphenoloxidase. This enzyme is responsible for the coagulation of the latex; this is an important function for the plant since the entire purpose of the rubber is to gum up the mouths of herbivorous insects. However, for humans extracting the rubber this coagulation can be a problem if it happens too soon. To that end, Gronover’s team has, using RNA interference, been able to silence the gene for this enzyme effectively preventing the formation of the polyphenoloxidase and therefore stopping the coagulation of the rubbery latex. This should make the rubber easier to extract. Perhaps the combination of a high yielding line and genetic techniques to simplify extraction may make the Russian dandelion a valuable agricultural product.

It was cost and supply issues which lead to the predominance of synthetic rubber — inferior though it may be — over natural, and in an ironic twist it could be those same factors that trigger its eclipse, and the return of natural rubber’s reign. Who knows, maybe some of us will become professional dandelion farmers in the next few years.