New approaches, based on ground simulation, to make possible the culture of plants in space (zero-g), and in the Moon and Mars gravity
The “round trip” spaceflight to Mars will expose the crew and the plants carried as part of their life support to 6 months of weightlessness, followed by a stay of 2-3 months (mínimum) in Mars (gravity 1/3g) until the position of planets allows the return travel, involving 6 additional months of zero-gravity. Upon their return to Earth, astronauts will have to re-adapt to the terrestrial gravity. Moon has a gravity magnitude lower than Mars, and could serve to facilitate adaptation.
New devices have been developed that allow reproducing on the ground the gravity of the Moon (1/6 of the Earth, 0.18g) and Mars (something more than 1/3, 0.37g). The biological validation of these devices was done by means of a study performed on plant seedlings of the model species Arabidopsis thaliana, which had previously been exposed to microgravity in successive experiments on the International Space Station (ROOT, GENARA, Seedling Growth) carried out by the same research group. The biological study shows that the rate of division and growth of Arabidopsis meristematic cells, their stem cells, are de-compensated by partial gravity reproducing alterations as strong, or even stronger than those observed previously in the experiments made on the Space Station, especially under the simulated Moon gravity. In turn, the simulated Mars gravity produces milder effects, with parameters closer to those recorded under 1g control conditions. An interesting preliminary conclusion that can be obtained from this study is that the threshold for sensing the gravity vector by plants can be established in a magnitude of this vector intermediate between the Moon and the Mars gravity. Additional research is needed to confirm or not these first impressions.
In addition, in a second work published in Scientific Reports, cell cultures of plants were analyzed to study the molecular mechanisms by which the cell proliferation rate is altered in different gravity conditions. These conditions were simulated microgravity, simulated Mars gravity and hypergravity, with a double value of the Earth (2g), to reproduce the situation in possible exoplanets. The latter condition was obtained by means of the Large Diameter Centrifuge located at the ESA-ESTEC Center. Among other assays, immunofluorescence experiments with an anti-methyl cytosine antibody to study the epigenetic alteration of DNA methylation show, consistent with the previous results, that microgravity causes a strong effect of increased methylation, the gravity of Mars produces an intermediate effect and the hypergravity practically does not modify the control pattern 1g. The existence of a change in the speed of the different cell cycle phases, which was proposed after space experiments, is now confirmed and analyzed in detail using in vitro cell cultures. This change results in premature cell division in space, which produces smaller cells. The precise mechanism by which the effect is produced remains under study. This paper has been the object of a separate comment in npj Microgravity Community by Kristopher James Kent.
Although the results obtained in the simulators must be validated in real microgravity, they can be useful in order to improve the growth conditions of the plants that will be part of the life support of astronauts in future space travels.
The two experiments have been developed in the context of international collaboration projects, funded in part by the European Space Agency (ESA) and in part by the Spanish and Dutch National Agencies.