Abstract
Plant cultivation on spacecraft or planetary outposts is a promising and actual perspective both for food and bioactive molecules production. To this aim, plant response to ionizing radiations, as an important component of space radiation, must be assessed through on-ground experiments due to the potentially fatal effects on living systems. Hereby, we investigated the effects of X-rays and γ-rays exposure on tomato “hairy root” cultures (HRCs), which represent a solid platform for the production of pharmaceutically relevant molecules, including metabolites and recombinant proteins. In a space application perspective, we used an HRC system previously fortified through the accumulation of anthocyanins, which are known for their anti-oxidant properties. Roots were independently exposed to different photon radiations, namely X-rays (250 kV) and γ-rays (Co60, 1.25 MeV), both at the absorbed dose levels of 0.5, 5, and 10 Gy. Molecular changes induced in the proteome of HRCs were investigated by a comparative approach based on two-dimensional difference in-gel electrophoresis (2D-DIGE) technology, which allowed to highlight dynamic processes activated by these environmental stresses. Results revealed a comparable response to both photon treatments. In particular, the presence of differentially represented proteins were observed only when roots were exposed to 5 or 10 Gy of X-rays or γ-rays, while no variations were appreciated at 0.5 Gy of both radiations, when compared with unexposed control. Differentially represented proteins were identified by mass spectrometry procedures and their functional interactions were analyzed, revealing variations in the activation of stress response integrated mechanisms as well as in carbon/energy and protein metabolism. Specific results from above-mentioned procedures were validated by immunoblotting. Finally, a morphometric analysis verified the absence of significant alterations in the development of HRCs, allowing to ascribe the observed variations of protein expression to processes of acclimation to ionizing radiations. Overall results contribute to a meaningful risk evaluation for biological systems exposed to extra-terrestrial environments, in the perspective of manned interplanetary missions planned for the near future.
Highlights
Plant cultivation is a key requirement for the success of longterm space missions
We evaluated the effects of both X- and γ-rays on “hairy root” cultures (HRCs), a recognized plant expression platform for the production of valuable molecules, offering advantages, e.g., containment, established cultivation conditions in hormone-free media, and product homogeneity, in the case of industrial-scale production of secondary metabolites (Mirapleix et al, 2013)
Plant colonization of land surface started around 460 million years ago, when the levels of β/γ-radiation in the Earth’s atmosphere were significantly higher than at present (Caplin and Willey, 2018). These environmental stresses have driven the evolution of terrestrial plant organisms, imposing the development of mechanisms of adaptation to radiations, which in all probability are partly maintained even in modern species
Summary
Plant cultivation is a key requirement for the success of longterm space missions. higher plants represent an essential component of bioregenerative life support systems (BLSS) for in situ production of food and pharmaceutical active molecules, not dependent on the supply at the launch or on periodic provision from Earth. Current knowledge on the response of plants to radiation is based mainly on studies conducted in areas affected by nuclear accidents (Møller and Mousseau, 2016). Hypotheses have been made to explain plants relative tolerance, such as higher efficiency in repairing DNA double strand breaks (Yokota et al, 2005) or higher basal rates of DNA methylation (Pecinka and Mittelsten Scheid, 2012). This higher resistance could be the result of evolutionary adaptation, which allowed plants to colonize land surface when ionizing radiations in the primordial Earth’s atmosphere were significantly higher than at present (Gensel, 2008). Physiological mechanisms that regulate this higher tolerance are not completely elucidated, in the perspective of plant growth during space missions (Arena et al, 2014) or in terrestrial environments contaminated by radiations (Danchenko et al, 2009)
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