Different types of ionizing radiation induce morpho-anatomical and antioxidant responses in Brassica rapa L. microgreens

The success of future long-term manned missions in Space is strictly related to the development and setup of sustainable closed artificial ecosystems, defined as Bioregenerative Life Support Systems (BLSSs). In these BLSSs, the cultivation of higher plants represents the core element, given its role in primary resources (e.g., oxygen, water) regeneration and in fresh food production, also helping to counteract the emergence of Space-induced diseases in astronauts. However, Space farming may be constrained by Space ionizing radiation for its influence on plant growth and biomass production, depending on radiation properties and plant intrinsic factors (e.g., type of radiation, dose, plant species, cultivar, developmental stage at the time of irradiation). 

This study aimed to evaluate the effects of the different types and doses of low and high-LET (Linear Energy Transfer) radiation on morpho-anatomical traits and antioxidant content of Brassica rapa L. subsp. sylvestris var. esculenta microgreens. Dry seeds were exposed to different doses (0-control, 0.3, 1, 10, 20, and 30 Gy) of X-rays (the reference Low-LET radiation) at Istituto Nazionale Tumori - IRCCS - Fondazione G. Pascale, and to two types of Heavy Ions, namely ¹²C and ⁵⁶Fe (to simulate the High-LET radiation) at different doses (0-control, 0.3, 1, 10, 20, and 25 Gy) at GSI Helmholtzzentrum für Schwerionenforschung GmbH. After the irradiation, seeds were sowed and microgreens were cultivated in a growth chamber under controlled environmental conditions, monitoring germination and survival, as well as growth performances. At the harvest, morpho-biometric traits, such as stem elongation, fresh and dry biomass, and total leaf area were measured. Leaf functional anatomical traits (e.g., lamina thickness, localization of phenolics, stomatal frequency) were quantified through light and epifluorescence microscopy and digital image analysis. The antioxidant charge of microgreens was evaluated considering antioxidant capacity, and polyphenols, chlorophylls, and carotenoid content. Results highlighted that the responses of microgreens, from irradiated seeds, were dose and radiation-type specific. This study furnished useful insights to evaluate plant radio-resistance at early stages of development, namely seedling establishment, that is a very critical phase in the plant life cycle. Gained information is useful to support the decision actions about the choice of suitable species to be cultivated in the BLSSs in Space and the definition of the shielding requirements for Space cultivation facilities.

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.