Abstract
BackgroundBiological systems respond to changes in both the Earth's magnetic and gravitational fields, but as experiments in space are expensive and infrequent, Earth-based simulation techniques are required. A high gradient magnetic field can be used to levitate biological material, thereby simulating microgravity and can also create environments with a reduced or an enhanced level of gravity (g), although special attention should be paid to the possible effects of the magnetic field (B) itself.ResultsUsing diamagnetic levitation, we exposed Arabidopsis thaliana in vitro callus cultures to five environments with different levels of effective gravity and magnetic field strengths. The environments included levitation, i.e. simulated μg* (close to 0 g* at B = 10.1 T), intermediate g* (0.1 g* at B = 14.7 T) and enhanced gravity levels (1.9 g* at B = 14.7 T and 2 g* at B = 10.1 T) plus an internal 1 g* control (B = 16.5 T). The asterisk denotes the presence of the background magnetic field, as opposed to the effective gravity environments in the absence of an applied magnetic field, created using a Random Position Machine (simulated μg) and a Large Diameter Centrifuge (2 g).Microarray analysis indicates that changes in the overall gene expression of cultured cells exposed to these unusual environments barely reach significance using an FDR algorithm. However, it was found that gravitational and magnetic fields produce synergistic variations in the steady state of the transcriptional profile of plants. Transcriptomic results confirm that high gradient magnetic fields (i.e. to create μg* and 2 g* conditions) have a significant effect, mainly on structural, abiotic stress genes and secondary metabolism genes, but these subtle gravitational effects are only observable using clustering methodologies.ConclusionsA detailed microarray dataset analysis, based on clustering of similarly expressed genes (GEDI software), can detect underlying global-scale responses, which cannot be detected by means of individual gene expression techniques using raw or corrected p values (FDR). A subtle, but consistent, genome-scale response to hypogravity environments was found, which was opposite to the response in a hypergravity environment.
Highlights
Biological systems respond to changes in both the Earth’s magnetic and gravitational fields, but as experiments in space are expensive and infrequent, Earth-based simulation techniques are required
We have studied the effect on the overall transcriptional state of Arabidopsis thaliana semi-solid cell cultures exposed to an environment of altered gravitational and magnetic forces for 200 min
An exposure of 200 min to intense magnetic fields alters the microarray-based transcriptional profile in Arabidopsis callus Figure 2 reflects the number of genes whose signal level changes in the different altered gravity/magnetic field environments, compared with the 1 g controls outside the simulators with a raw limma p value < 0.01 and a false discovery rate (FDR) corrected RankProd p value < 0.05
Summary
Biological systems respond to changes in both the Earth’s magnetic and gravitational fields, but as experiments in space are expensive and infrequent, Earth-based simulation techniques are required. A high gradient magnetic field can be used to levitate biological material, thereby simulating microgravity and can create environments with a reduced or an enhanced level of gravity (g), special attention should be paid to the possible effects of the magnetic field (B) itself. Since the beginning of life on Earth, organisms have lived under the influence of the Earth’s physical parameters including its almost constant gravitational and magnetic fields. Evolution has had to provide a number of different solutions to meet the mechanical may significantly affect astronauts manning the first space colonies, and the development of plants, which would be an essential part of life support systems. The exposure of Arabidopsis seedlings to magnetic fields in excess of about 15 T for 6.5 h has been linked with 2.5 fold changes in the expression levels of 114 genes [14]
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