The tyres of the future may be made from dandelions
Tremble, Michelin, tremble
OTHER than being an ingredient of the more recherché sorts of salad, herbal tea or wine, dandelions are pretty useless plants. Or, at least, they were. But one species, a Russian variety called Taraxacum kok-saghyz (TKS), may yet make the big time. It produces molecules of rubber in its sap and if two research programmes, one going on 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, for nothing artificial yet matches natural rubber’s resilience and strength. This is because natural-rubber molecules, the product of a stepwise synthesis by enzymes, have a more regular structure than the artificial ones made by chemical engineering. Around a fifth of an average car tyre is therefore made of natural rubber. In an aeroplane tyre that figure can be more than four-fifths. Moreover, the price of synthetic rubber is tied to that of the oil from which it is made, rendering it vulnerable to changes in the oil price. Because oil is likely to become more costly in the future, natural rubber looks 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. A disease called leaf blight means the trees have to be spaced widely. Even in Asia, currently blight-free, planting new rubber trees often means cutting down rainforest, to general disapproval. 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 therefore has obvious appeal.
To this end, Christian Schulze Gronover of the Fraunhofer Institute for Molecular Biology and Applied Ecology 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 has appeared independently in plants as diverse as trees, guayule and dandelions, is that it gums up the mouthparts of herbivorous insects. Human users, however, do not want it to coagulate too soon, and Dr Schulze Gronover has found a way to switch polyphenoloxidase off, using a technique called RNA interference. This intercepts and destroys the molecular messengers that carry instructions from the polyphenoloxidase gene to make the enzyme, meaning that rubber can be extracted more easily from the plant.
Meanwhile, in America Matthew Kleinhenz of Ohio State University is working on increasing the yield of rubber from TKS. Dr Kleinhenz is doing things the old-fashioned way, growing different strains of TKS, grinding up the roots (where most of the sap is found) to see which have the highest rubber content, and crossbreeding the winners. His aim is to create a plant that is both high-yielding and has roots chunky enough to be harvested mechanically by the sort of device now used to pick carrots.
Combining the two approaches—high-tech bioengineering and low-tech plant breeding—may produce that rarity in the modern world, 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, briefly, been overshadowed by the transient availability of cheap oil.