Effect of heavy ions on development, photosynthesis and fruits antioxidant production in Solanum lycopersicum L. ‘Microtom’ plants: a space perspective.

ABSTRACT: A sustainable human space exploration, including long-duration manned missions, needs some essential requirements, among which one of the most challenging is the habitat management, given the impossibility of providing large amount of resources from Earth for astronauts’ survival. In this perspective the realisation of self-sufficient closed habitats (Bioregenerative Life Support Systems - BLSSs) represents a challenge for scientists. In such environments higher plants contribute to air regeneration, water recovery, and food production. When planning the use of plants in BLSS, specific constraints must be kept in mind. Among these limits, ionising radiation could have the most deep implications. In this study, we explore whether low doses of heavy ions, namely Ca 25 Gy, delivered at the seed stage, may induce positive outcomes on growth and functional traits in plants of Solanum lycopersicum L.‘Microtom’. This cultivar was selected as a model crop for its dwarf size and short life-cycle. We hypothesized that not-lethal doses of heavy ions can induce favourable effects in photosynthesis, biomass production and antioxidant properties of fruits. After seed irradiation, plant growth was followed from germination up to fructification. Morphological parameters, photosynthetic efficiency, leaf anatomical traits and antioxidant production in leaves and fruits were analysed. The results showed that irradiation of seeds with Ca ions does not induce anomalies in seed germination, but leads to a more compact plant size, reducing plant height. As regards photosynthesis, the irradiation of seeds promoted in adult plants an increase of photosystem II photochemistry and higher levels of D1 protein and photosynthetic pigment content compared to control. Plants germinated from irradiated seeds have leaves containing smaller cells and a lower number of chloroplasts compared to not irradiated samples. Finally, the same plants produced fruits with an higher amount of ascorbic acid, carotenoids and anthocyanins. These last results should be further investigated since these compounds could strengthen the antioxidant defences of astronauts undergoing long space missions. Indeed, plants may perceive the shielded doses of ionising radiation in BLSSs as a stimulus to produce antioxidants and secondary metabolites in order to protect their cells.