Novel, Moon and Mars, partial gravity simulation paradigms and their effects on the balance between cell growth and cell proliferation during early plant development

Aránzazu Manzano,Leonardus A Den Toom,Martijn Visser,Guus Borst,F Javier Medina,Raúl Herranz,Jack J W A Van Loon,Sjoerd Te Slaa

doi:10.1038/s41526-018-0041-4

Abstract

Clinostats and Random Positioning Machine (RPM) are used to simulate microgravity, but, for space exploration, we need to know the response of living systems to fractional levels of gravity (partial gravity) as they exist on Moon and Mars. We have developed and compared two different paradigms to simulate partial gravity using the RPM, one by implementing a centrifuge on the RPM (RPMHW), the other by applying specific software protocols to driving the RPM motors (RPMSW). The effects of the simulated partial gravity were tested in plant root meristematic cells, a system with known response to real and simulated microgravity. Seeds of Arabidopsis thaliana were germinated under simulated Moon (0.17 g) and Mars (0.38 g) gravity. In parallel, seeds germinated under simulated microgravity (RPM), or at 1 g control conditions. Fixed root meristematic cells from 4-day grown seedlings were analyzed for cell proliferation rate and rate of ribosome biogenesis using morphometrical methods and molecular markers of the regulation of cell cycle and nucleolar activity. Cell proliferation appeared increased and cell growth was depleted under Moon gravity, compared with the 1 g control. The effects were even higher at the Moon level than at simulated microgravity, indicating that meristematic competence (balance between cell growth and proliferation) is also affected at this gravity level. However, the results at the simulated Mars level were close to the 1 g static control. This suggests that the threshold for sensing and responding to gravity alteration in the root would be at a level intermediate between Moon and Mars gravity. Both partial g simulation strategies seem valid and show similar results at Moon g-levels, but further research is needed, in spaceflight and simulation facilities, especially around and beyond Mars g levels to better understand more precisely the differences and constrains in the use of these facilities for the space biology community.

Highlights

Since the beginning of life on Earth, organisms have evolved in an environment of physico-chemical factors, many of them changing while a few remained constant or almost constant, such as the gravitational and magnetic fields.[1]
We evaluated the status of the meristematic competence in the roots of young Arabidopsis thaliana seedlings
Two ways to simulate a net partial gravity level based on the Random Positioning Machine (RPM) have been developed and successfully used in this plant biology study, either by the implementation of a hardware (RPMHW) or by a software (RPMSW) simulation paradigm

Summary

Introduction

Since the beginning of life on Earth, organisms have evolved in an environment of physico-chemical factors, many of them changing (pressure, temperature, humidity,...) while a few remained constant or almost constant, such as the gravitational and magnetic fields.[1]. Tampering with a force like gravity can only be done manipulating its magnitude or its direction because one cannot cancel the force of gravity, for long periods, while remaining on the surface of a celestial body like Earth. For aircraft PF this is in the order of ten to some 50 s depending on the aircraft and this time increases up to some 13 min by using ballistic rockets like the MAXUS system.[5] Note that for the latter two conditions periods of hypergravity are involved which might distort the actual microgravity effect.[6] An alternative is to compensate gravity by levitating individual atoms by means of a strong gradient magnetic field.[7,8] one has to take into account the strong magnetic field as such, this is relevant for the case of biological experiments.[9,10]

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