Question: where does the great majority of the rubber in rubber tyres* (tires for our American cousins…) come from? Answer: natural rubber from the Pará rubber tree, Hevea brasiliensis (in the famously latex-exuding spurge family, the Euphorbiaceae), primarily.
Non-natural – so-called synthetic** – rubber is also made, from by-products of the petroleum industry, and whose price is in part determined by the volatile crude oil market. With that important economic dimension, concerns such as the susceptibility of rubber plantations to disease or other biotic and abiotic factors, and keenness for nations to avoid rubber-reliance on foreign sources, natural alternatives to pará rubber are sought.
Of the many contenders in this category, two candidates are dandelion (Taraxacum species) and lettuce (Lactuca species), both members of the daisy family, the Asteraceae (synonym Compositae – for my more traditional/older readers…). Understanding the biology – and molecular biology – of those laticiferous taxa is therefore important both to understanding how the plants make the rubber and its human exploitation.
Appropriately, keeping the hitherto untapped potential of both of those two plants in contention, is a quartet of recent papers. Studying Taraxacum brevicorniculatum (which taxon, and although there’s no suggestion that this has happened here, is apparently sometimes mistaken for T. kok-saghyz), Janina Epping et al. show that a rubber transferase activator is necessary for natural rubber biosynthesis in dandelion. Natalie Laibach et al. identified a T. brevicorniculatum rubber elongation factor protein that is localized on rubber particles and promotes rubber biosynthesis. Using biochemical and genetic techniques, Jared Bell et al. have evaluated prickly lettuce (L. serriola) both as a rubber producer, and one that could be grown in continental USA, in eastern Washington, which could help allay fears over the USA’s rubber-dependency from ‘abroad’. And Yang Qu et al. demonstrate that a homolog of human Nogo-B receptor (which modulates blood vessel formation) interacts with cis-prenyltransferase and is necessary for natural rubber biosynthesis in L. sativa. As the USA aspires to a state of home-grown rubber-independency, so too does the European Union with project DRIVE4EU exploring the uses of both Russian dandelion (T. kok-saghyz) and the flowering shrub guayule (Parthenium argentatum, also in the Asteraceae). And all this against a background of concerns over sustainability of worldwide rubber supplies.
* Other well-known rubber products include erasers (‘rubbers’ in the UK) and condoms (potentially, and comically confusingly, called ‘rubbers’ in the USA), both of which have been in the news recently. The former having been designated ‘an instrument of the devil’ – commonly used to rub out/erase ‘mistakes’, rubbers should be banned in the classroom according to King’s College (London, UK) visiting professor and cognitive scientist Guy Claxton (mistakes are your friends, they are your teachers, not something to be ashamed of and erased…). The latter have been highlighted in a news item promoting a competition sponsored by the Bill & Melinda Gates Foundation to create a better condom that is more likely to be used as a contraceptive method by men. NB, in the interests of even-handedness, we should point out that female condoms are also available.
** But, doesn’t all rubber have to be synthesised, whether by nature within the plant or by humans in laboratories or petrochemical plants…?[To remind you just how beautiful taraxaca are, Brian Johnson has a photofest of dandelion images on his website. For more on dandelion biology and ecology, check out The Plant Guy, Kate Bradbury at the Guardian’s Wildlife Gardening blog and Sarah Shailes at her Plant Scientist blogsite. And for a fusion of dandelion nature and art, why not visit Studio Drift’s Fragile Future Concrete Chandelier? – Ed.]