Can be Solanum lycopersicum L. cv ‘Micro-Tom’ a good candidate for growth in Space? Testing the effects of High-LET ionizing radiation on plant growth, photosynthesis and antioxidants

The possibility to cultivate plants in Space represents an ongoing challenge because in extraterrestrial environments, plant growth is controlled by factors, some of which are also acting on Earth (e.g. temperature, relative humidity, light) while others are peculiar such as altered gravity in addition to a profoundly different ionizing radiation (IR) field (De Micco et al., 2011). In particular, exposure to Space IR may determine several outcomes depending on the dose, radiation quality (high vs. low LET), exposure rate (acute vs. chronic), but also by the intrinsic characteristics of the organism, such as species, cultivars, developmental stage, structure of organs and tissues and genetic traits (De Micco et al., 2011). Generally, plant response to IR is manifestly dose-dependent with irreparable damage at high doses, sublethal consequences at intermediate levels and stimulatory effects at low dose (De Micco et al., 2011; Arena et al., 2014). In this study we explore the possibility that low doses of heavy ions, namely C ions at dose of 25 Gy delivered at seed stage, may exert beneficial effects on Solanum Lycopersicum L. cv ‘Micro-Tom’ on physiological, biochemical and anatomical traits, promoting the fruit ripening and quality. This would have important consequences in the view of its utilization on board of the Bioregenerative Life Support Systems (BLSSs) as food for crew. For this purpose, the plant life cycle from germination to fruit harvesting was monitored in terms of plant growth, photosynthetic efficiency, leaf anatomical traits and antioxidant production in leaf and fruits. The irradiation did not affect plant germination. Plants from irradiated seeds showed reduced height and a more compact size. The PSII quantum yield as well as the electron transport rate was promoted in irradiated compared to control plants. These data are consistent with a high level of D1 protein and photosynthetic pigment content in the leaves. As regards fruit, plants from irradiated seeds showed a significantly higher content of ascorbic acid, carotenoids and anthocyanins.