Impact of gamma-rays on seed germination/short-term storage in four native alpine species: correlation with free radical and antioxidant profiles

In this study, the impact of gamma radiation on seeds was investigated in four native alpine species, Campanula barbata L., Cirsium spinosissinum (L.) Scop., Plantago alpina L., and Silene vulgaris (Moench) Garcke. Seeds were gamma-irradiated with 100 and 200 Gy total doses delivered at a dose rate of 2.7 Gy min-1. Irradiated and non-irradiated seeds were used immediately, and subsequently 7 and 14 days after drying (15% Relative Humidity, 15°C) to assess their response to standard seed bank processing. Germination rates, seedling length and weight, antioxidant activity and phenolics content were measured, while free radical accumulation profiles were acquired by electron paramagnetic resonance (EPR). Germination was only hampered in irradiated C. barbata seeds. C. barbata and C. spinosissinum seedlings obtained from irradiated seeds suffered a decrease in length and weight, while growth was not affected in P. alpina and S. vulgaris, when compared to non-irradiated control. Although profiles of seed antioxidant activity were not influenced immediately after gamma-irradiation, subsequent drying under seed bank standards induced changes in seed antioxidant activity, depending on the species. According to EPR data, C. barbata and C. Spinosissinum seeds revealed high free radical levels in non-irradiated samples, which were further enhanced by gamma-irradiation. An opposite behaviour was observed in P. alpina and S. vulgaris. The four alpine species showed different profiles of gamma-ray sensitivity. The reported data encourage future research to test inter-specific variability in the plant response to gamma-rays based on a multidisciplinary approach which integrates environmental data. Considering that seeds of alpine plants are short-lived in storage, gamma-irradiation could emerge as a promissory priming tool for native endangered species.