Radioresistance of dwarf bean plants irradiated with C and Ti heavy ions

Plant cultivation in Space is a challenge for biology. In this context, preliminary studies with high energetic particles provide information about the capability of plants to withstand ionizing radiation in space. Non-lethal levels of high-LET ionizing radiation may stimulate physiological and morphological traits in plants, increasing their ability to be cultivated in extraterrestrial environments. In this study, we test the radioresistance of Dolichos melanophtalmus DC. (dwarf bean) irradiated at seed stage with low doses of heavy ions, namely C 1Gy, C 10 Gy, Ti 1 Gy and Ti 10 Gy. These doses, lethal for mammalian cells resulted not as dangerous for plants. After germination, alterations in growth were recorded by morphometric analysis; the photosynthetic efficiency was evaluated by chlorophyll a fluorescence emission measurements and determination of photosynthetic pigments’ content.The occurrence of oxidative stress and plant capability to withstand it were tested by measuring the intracellular H2O2 level, the ascorbic acid content and the poly(ADPribose) polymerase (PARP) activity. The irradiation of the seeds with different types of heavy ions and doses did not prevent either seed germination or the completion of plant life cycle; indeed irradiated plants were able to produce a new generation of seeds. Stimulatory effects on plant height were observed at Ti10 Gy, whereas C 10 Gy treatment determined a decrease in plant growth. The dose of C 10 Gy also reduced plant photochemistry and pigment content compared to other treatments, indicating the occurrence of damages at the photosystem level. However, in C 10 Gy treated plants the increase in intracellular H2O2 concentration, together with the rise in ascorbic acid and PARP activity, suggests the occurrence of a radio-induced oxidative stress mitigated by plant capability to activate the defense mechanisms successfully.