The Growth of Soybean (Glycine max) Under Salt Stress Is Modulated in Simulated Microgravity Conditions

The role of a simulated microgravity environment on soybean growth was investigated. The root grew more under simulated microgravity conditions than in the presence of gravity. However, root shortening due to salt stress did not occur in simulated microgravity conditions. To reveal these mechanisms by simulated microgravity environment on soybean root, a proteomic analysis was conducted. Proteomic analysis revealed that among 1547 proteins, the abundances of proteins related to phytohormone, oxidative stress, ubiquitin/proteasome system, cell organization, and cell wall organization were altered under stimulated microgravity compared with gravity. Membrane-localized proteins and redox-related proteins were inversely correlated in protein numbers due to salt stress under gravity and the simulated microgravity condition. Proteins identified by proteomics were validated for protein accumulation by immunoblot analysis. Superoxide dismutase and ascorbate peroxidases, which are reactive oxygen species-scavenging proteins, increased in soybean root under salt stress but not in the simulated microgravity conditions even under stress. The accumulation of 45 kDa aquaporin and 70 kDa calnexin in soybean root under salt stress were increased in the simulated microgravity conditions compared to gravity. These findings suggest that soybean growth under salt stress may be regulated through improved water permeability, mitigation of reactive oxygen species production, and restoration of protein folding under simulated microgravity conditions.