Dandelion Tires

Other than being an ingredient of upscale salads, dandelions are pretty useless plants. But one species, Taraxacum kok-saghyz (TKS), may yet make the big time. It produces molecules of rubber in its sap, and—if two research programs, one in Germany and one in America, come to fruition—it could supplement or even replace the traditional rubber tree, Hevea brasiliensis.

Despite the invention of synthetic rubbers, there is often no good substitute for the real thing. This is because natural-rubber molecules have a more regular structure than artificial ones. For this reason, around one-fifth of an average car tire is made of natural rubber. Moreover, the price of synthetic rubber is tied to that of the oil from which it is made, rendering it vulnerable to changing
oil prices.

Because oil is likely to become more costly in the future, natural rubber looks to be an attractive alternative, from an economic point of view as well as an engineering one.

Natural rubber has problems, though. Growing Hevea in the Americas is hard. In Asia, planting new rubber trees often means cutting down rainforest. And trees, being large, take time to grow to the point where they can yield a crop. A smaller plant that could be harvested for its rubber thus has obvious appeal.

Which is where TKS comes in. Dandelions are robust, fast-growing plants that can be pulled up for processing and resown easily, possibly yielding two harvests a year. If they could be turned into usable crops, they could outstrip even Hevea.

To this end, Christian Schulze Gronover of the Fraunhofer Institute in Aachen, Germany, and his colleagues have identified the genes that allow TKS to produce usable rubber. In particular, they have discovered an enzyme called polyphenoloxidase that is responsible for making its rubbery sap coagulate.

From the plant’s point of view, this coagulation is a good thing. The evolutionary purpose of rubber—and the reason why it appears independently in plants as diverse as trees and dandelions—is to gum up the mouth parts of herbivorous insects. Human users, however, do not want it to coagulate too soon, and Schulze Gronover has found a way to switch off polyphenoloxidase by using a technique called RNA interference. This makes it easier to extract rubber from the plant.

Meanwhile, Matthew Kleinhenz of Ohio State University is working on increasing the yield of rubber from TKS. Kleinhenz is doing things the old-fashioned way, growing different strains of TKS, grinding up the roots (where sap is found) to see which have the highest rubber content, and cross-breeding the winners. His aim is to create a plant that is high-yielding and has roots chunky enough to be harvested mechanically.

Combining the two approaches—high-tech bioengi-neering and low-tech plant breeding—may produce a whole new crop species. It would also mark a step on a journey that some see as the way forward: a return to the use of plant-based products that have been overshadowed by the availability of cheap oil. ❧

©2009 The Economist Newspaper Ltd, London

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