Lichens, thale cress, tobacco, the great survivors…

It is often said that cockroaches are one of the hardiest of animals, allegedly able to withstand a nuclear holocaust. Well, serious contenders amongst the plant-like critters are lichens, thale cress and tobacco. Rhizocarpon geographicum and Xanthoria elegans have both survived a 1.5-year extraterrestrial sojourn aboard the International Space Station according to work by Silvano Onofri et al.

During their 2008–9 space odyssey the lichens were exposed to space vacuum (as low as 10^–7 Pa), galactic cosmic radiation (£ 190 mGy), the full spectrum of solar radiation (l > 110 nm), and temperatures from –21.5 to 59.6 °C. Impressive? Yes, but even more impressive is the revelation by David Tepfer et al. that seeds of Arabidopsis thaliana and Nicotiana tabacum exposed to similar conditions also survived (for 558 days), with germination rates of 23 % and 44 %, respectively, back on the ground. In that latter study the authors concluded that ‘a naked, seed-like entity could have survived exposure to solar UV radiation during a hypothetical transfer from Mars to Earth’. I’m not sure if that means that it’s the Martians we must thank for the ‘gift of Arabidopsis’, or whether the return journey is also possible and that if we ever get to Mars at least the plant biologists will be able to continue to study their beloved thale cress (and tobacco – and maybe even lichens…)!