The study of morpho-anatomical and biochemical traits on irradiated microgreens to unlock crop potential in Space

In the upcoming years, agriculture will have a central role not only in feeding a growing population worldwide, but also in Space-related research, through the implementation of protected cultivation systems. To make it possible, it is fundamental to understand plants’ ability to cope with a dynamic environment, made worst by harsh Space conditions including microgravity and ionizing radiation.Plant plasticity in adaptation relies on the development of both structural and physiological traits, which are deeply influenced by the environment; therefore, leaf morpho-anatomical traits are critical for balancing plant water and CO2 exchange and determine the efficiency of CO2 diffusion within the mesophyll. Their relationship has been widely studied; however, it remains unclear at what extent leaf anatomical traits may drive leaf hydraulic and photosynthetic acclimation to Space environmental stressors.Previous studies have proven that ionizing radiation can induce positive, null or negative effects depending on the radiation type, dose and exposure (acute or chronic) as well as plant developmental stage and species.In this study, we compared functional, anatomical (e.g., leaf area, leaf dry matter content, leaf mass per area, stomatal and vein size and density, mesophyll organization, chloroplast distribution) and biochemical traits (e.g. chlorophyll and carotenoids content, polyphenols, ascorbic acid) of brassica microgreens (Brassica rapa L. subsp. sylvestris var. esculenta) exposed to three different types of radiation (X-rays, Carbon ion 12C, Iron ion 56Fe) at the same doses (0-control, 0.3, 1, 10, 20, and 25 Gy). Irradiation took place at the GSI Helmholtzzentrum für Schwerionenforschung GmbH, and then microgreens were cultivated in a growth chamber under controlled condition. Microgreens were chosen as study model for two main reasons. First, microgreens are good candidates for the diet integration of astronauts because they are rich in nutraceutical compounds and can be cultivated directly in Space with very low input resources. From a fundamental science viewpoint, understanding the morpho-functional responses of microgreens is needed because at this stage of development plants are very vulnerable: overcoming the microgreens stage may represent a bottleneck in the cultivation of adult plants in bioregenerative life support systems.The results suggest the different radiation type and doses determined alterations in morpo-anatomical and biochemical traits which may determine the limits of crop responses and biomass production. These findings should be considered when studying plant adaptation to Space environment, trying to optimize plant growth in controlled environment to achieve the sustainability of the system. Part of the results presented here is based on the experiment Bio_08_DeMicco, which was performed at the SIS18 at the GSI Helmholtzzentrum fuer Schwerionenforschung, Darmstadt (Germany) in the frame of FAIR Phase-0.