Plant Adaptation to Microgravity Environment and Growth of Plant Cells in Altered Gravity Conditions

Abstract

This paper introduces one of the plant biology experiments, “Biological effects and the signal transduction of microgravity stimulation in plants”, carried out on the SJ-10 recoverable microgravity experimental satellite (SJ-10 satellite). The experimental equipment, experimental process and some results of follow-up analysis are described. When the Arabidopsis seedlings returned to the ground after 11 days of microgravity, their leaf area was larger than that of the ground control. The whole genome methylation analysis was also performed by using the Arabidopsis seedlings chemically fixed with RNAlater in space after 60 h of growth under microgravity environment. The results demonstrated that the epigenetic differences in Arabidopsis seedlings exposed to microgravity. The Arabidopsis genome exhibits lower methylation levels in the CHG, CHH and CpG contexts under microgravity conditions. Microgravity stimulation was related to altered methylation of a number of genes, including DNA methylation-associated genes, hormone signaling related genes, cell wall modification genes and transposable elements (TEs). Relatively unstable DNA methylation of TEs was responsible for the induction of active transposons. These observations suggest that DNA demethylation within TEs may change the function exertion of transposons in response to microgravity conditions. In order to further understand the relationship between plant growth, epigenetic changes and plant adaptation to microgravity environment, the biological effects of gravity on plant cells and seedlings based on data obtained from both ground-based research and space experiments on board the Chinese satellite “SJ-10” and the Chinese spaceship “Shenzhou-8” are discussed in this chapter. The data demonstrate the impact of direction and intensity changes of gravity on cell wall metabolism during plant gravitropism and on cells in the state of weightlessness. It is assumed that the maintenance of cell shape requires a balance between cell wall rigidity and cell turgor. When the cell turgor is greater than the rigidity, the balance is broken and may lead to increasing cell volume. Therefore, changes in gravity may affect cell growth by influencing the balance between cell wall rigidity and cell turgor. As a result, the supporting tissue system of plants is weakened in the process of adapting to the microgravity environment, leading to the disruption of the mechanical balance in cells, which may further affect the plant growth and development. In summary, the results of these investigations are beneficial for understanding the mechanism of plant adaptation to microgravity and improve strategies to allow plants to adapt to space.