Glucosinolate and Sugar Profiles in Space-Grown Radish

The quest to establish permanent outposts in space, the Moon, and Mars requires growing plants for nutrition, water purification, and carbon/nutrient recycling, as well as the psychological well-being of crews and personnel on extra-terrestrial platforms/outposts. To achieve these essential goals, the safety, quality, and sustainability of plant material grown in space should be comparable to Earth-grown crops. In this study, radish plants were grown at 2500 ppm CO₂ in two successive grow-outs on the International Space Station and at similar CO₂ partial pressure at the Kennedy Space Center. An additional control experiment was performed at the University of Louisiana Lafayette laboratory, at ambient CO₂. Subsequent analyses of glucosinolate and sugar species and content showed that regardless of growth condition, glucoraphasatin, glucoraphenin, glucoerucin, glucobrassicin, 4-hydroxyglucobrassicin, 4-methoxyglucobrassicin, and three aliphatic GSLs tentatively assigned to 3-methylpentyl GSL, 4-methylpentyl GSL, and n-hexyl GSL were present in all examined plants. The most common sugars were fructose, glucose, and sucrose, but some plants also contained galactose, maltose, rhamnose, and trehalose. The variability of individual secondary metabolite abundances was not related to gravity conditions but appeared more sensitive to CO₂ concentration. No indication was found that radish cultivation in space resulted in stress(es) that increased glucosinolate secondary metabolism. Flavor and nutrient components in space-grown plants were comparable to cultivation on Earth.