The combined effects of real or simulated microgravity and red-light photoactivation on plant root meristematic cells
Red light is able to compensate for deleterious effects of microgravity on root cell growth and proliferation. Partial gravity combined with red light produces differential signals during the early plant development.
Light and gravity are environmental cues used by plants throughout evolution to guide their development. We have investigated the cross-talk between phototropism and gravitropism under altered gravity in space. The focus was on the effects on the meristematic balance between cell growth and proliferation, which is disrupted under microgravity in the dark. In our spaceflight experiments, seedlings of three Arabidopsis thaliana genotypes, namely the wild type and mutants of phytochrome A and B, were grown for 6 days, including red-light photoactivation for the last 2 days. Apart from the microgravity and the 1g on-board control conditions, fractional gravity (nominally 0.1g, 0.3g, and 0.5g) was created with on-board centrifuges. In addition, a simulated microgravity (random positioning machine, RPM) experiment was performed on ground, including both dark-grown and photostimulated samples. Photoactivated samples in spaceflight and RPM experiments showed an increase in the root length consistent with phototropic response to red light, but, as gravity increased, a gradual decrease in this response was observed. Uncoupling of cell growth and proliferation was detected under microgravity in darkness by transcriptomic and microscopic methods, but red-light photoactivation produced a significant reversion. In contrast, the combination of red light and partial gravity produced small but consistent variations in the molecular markers of cell growth and proliferation, suggesting an antagonistic effect between light and gravity signals at the early plant development. Understanding these parameters of plant growth and development in microgravity will be important as bioregenerative life support systems for the colonization of the Moon and Mars.
KeywordsArabidopsis Cell growth Cell proliferation Fractional gravity Spaceflight Tropisms
European Modular Cultivation System
International Space Station
random positioning machine
wild type of the Landsberg erecta ecotype of Arabidopsis thaliana
Funding for this study was provided mainly by the Spanish National Plan for Research and Development (MINECO-ERDF co-funding) Grant ESP2015-64323-R to FJM. The access to ISS and RPM facilities was granted by ESA-ELIPS ILSRA-2009-0932 to FJM and GBF Program GIA Project (contract# 4000105761) to RH. This research was supported also by grants (NNX12A0656 and 80NSSC17K0546) from NASA to JZK and the French Space Agency—CNES to ECD and VPL. MAV and AM were recipients of grants of the Spanish National Program for Young Researchers Training (Refs. BES-2010-035741 and BES-2013-063933, respectively). We would like to thank the skillful technical assistance of Mrs. Mercedes Carnota (CIB-CSIC), the fine support of NASA’s Ames Research Center in the use of TROPI hardware, and the European Space Agency and the Norwegian User Support and Operations Center (N-USOC) for their continuous support throughout the entire “Seedling Growth” space project. Finally, we would like to thank the astronauts on board the ISS for their work, without whom these experiments would have not been possible.
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