Abstract
BackgroundCell growth and cell proliferation are intimately linked in the presence of Earth’s gravity, but are decoupled under the microgravity conditions present in orbiting spacecraft. New technologies to simulate microgravity conditions for long-duration experiments, with stable environmental conditions, in Earth-based laboratories are required to further our understanding of the effect of extraterrestrial conditions on the growth, development and health of living matter.ResultsWe studied the response of transgenic seedlings of Arabidopsis thaliana, containing either the CycB1-GUS proliferation marker or the DR5-GUS auxin-mediated growth marker, to diamagnetic levitation in the bore of a superconducting solenoid magnet. As a control, a second set of seedlings were exposed to a strong magnetic field, but not to levitation forces. A third set was exposed to a strong field and simulated hypergravity (2 g). Cell proliferation and cell growth cytological parameters were measured for each set of seedlings. Nucleolin immunodetection was used as a marker of cell growth. Collectively, the data indicate that these two fundamental cellular processes are decoupled in root meristems, as in microgravity: cell proliferation was enhanced whereas cell growth markers were depleted. These results also demonstrated delocalisation of auxin signalling in the root tip despite the fact that levitation of the seedling as a whole does not prevent the sedimentation of statoliths in the root cells.ConclusionsIn our model system, we found that diamagnetic levitation led to changes that are very similar to those caused by real- [e.g. on board the International Space Station (ISS)] or mechanically-simulated microgravity [e.g. using a Random Positioning Machine (RPM)]. These changes decoupled meristematic cell proliferation from ribosome biogenesis, and altered auxin polar transport.
Highlights
Cell growth and cell proliferation are intimately linked in the presence of Earth’s gravity, but are decoupled under the microgravity conditions present in orbiting spacecraft
In an orbiting spacecraft such as the International Space Station, weightlessness is maintained for long periods of time, but access to the platform is severely constrained in terms of the number of experiments that can be performed, the availability of crew time for experimentation and cost
Morphometric analysis of the seedlings and root meristems Seedling length after 2 and 4 days of growth was used as the first parameter for estimating cell growth and proliferation
Summary
Cell growth and cell proliferation are intimately linked in the presence of Earth’s gravity, but are decoupled under the microgravity conditions present in orbiting spacecraft. In an orbiting spacecraft such as the International Space Station, weightlessness is maintained for long periods of time, but access to the platform is severely constrained in terms of the number of experiments that can be performed, the availability of crew time for experimentation and cost. These limitations have encouraged the development of ground-based systems to simulate modified gravity conditions, such as 2D-clinostats, Random Positioning Machines (RPMs), and adapted centrifuges. We use an alternative ground-based technique, which exploits the force exerted on diamagnetic material when exposed to a strong and inhomogeneous magnetic field [5,6,7]
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