Radiation environment in exploration-class space missions and plants’ responses relevant for cultivation in Bioregenerative Life Support Systems

Abstract

For deep space exploration, radiation effects on astronauts, and on items fundamental for life support systems, must be kept under a pre-agreed threshold to avoid detrimental outcomes. Therefore, it is fundamental to achieve a deep knowledge on the radiation spatial and temporal variability in the different mission scenarios as well as on the responses of different organisms to space-relevant radiation. In this paper, we first consider the radiation issue for space exploration from a physics point of view by giving an overview of the topics related to the spatial and temporal variability of space radiation, as well as on measurement and simulation of irradiation, then we focus on biological issues converging the attention on plants as one of the fundamental components of Bioregenerative Life Support Systems (BLSS). In fact, plants in BLSS act as regenerators of resources (i.e. oxygen production, carbon dioxide removal, water and wastes recycling) and producers of fresh food. In particular, we summarize some basic statements on plant radio-resistance deriving from recent literature and concentrate on endpoints critical for the development of Space agriculture. We finally indicate some perspective, suggesting the direction future research should follow to standardize methods and protocols for irradiation experiments moving towards studies to validate with space-relevant radiation the current knowledge. Indeed, the latter derives instead from experiments conducted with different radiation types and doses and often with not space-oriented scopes.

Growth, Anatomical, and Biochemical Responses of the Space Farming Candidate Brassica rapa L. Microgreens to Low-LET Ionizing Radiation

“…This stage represents a very delicate phase in the plant life cycle because after the break of dormancy, the plant is characterized by active meristems and morphogenesis, particularly vulnerable to abiotic stress, which may weaken the seedling establishment [59]. In space, the presence of ionizing radiation [29,30,44] may influence early morphogenesis in plants [45][46][47]. Previous research has demonstrated that low doses of X-rays may generally induce positive effect on the viability, germination, and growth of the seeds, while high doses may reduce or hamper these delicate phases [35,60,61].…”

“…In the experiments of radiobiology performed on Earth, considering the reduced possibility to recreate all the radiation spectrum and their dose intensity, particle accelerators are used. In these facilities, dose rates of many orders of magnitude higher than those in space are normally used to reduce the duration of the trials and to estimate the possible effects that would occur with lower doses over a longer period of time [44].…”

Plant and microbial science and technology as cornerstones to Bioregenerative Life Support Systems in space

“…Plants are the primary food producers for humans on Earth and have the potential to accomplish the same task in space. Furthermore, by consuming carbon dioxide and producing oxygen through photosynthesis, purifying water from the collection of transpired water, and having a role in waste recycling, they are well-suited for the regeneration of resources 15 . Although regeneration of resources in short-term missions would be a “nice-to-have” requirement, it becomes a “must-have” in long-term missions where resupply from Earth would not be feasible and where initial launch mass to carry all consumables would be prohibitive.…”

Perspectives for plant biology in space and analogue environments

“…different species/cultivars, target organs/tissues). Recently, more attention has been dedicated to the effect of ionizing radiation (IR) so far as it represents a clear challenge for exploratory-class missions 14 . Altered gravity and exposure to IR can induce changes in gene expression, cell proliferation and differentiation, signalling and physiological processes (see precise data and references in the following paragraphs).…”

“…Outside Low Earth Orbit, IR is variable in space and time and can severely constrain organisms’ growth 3 , 14 . IR can cause direct damage to the structures encountered, but also indirect due to the generation of reactive oxygen species (ROS) 64 , 65 .…”