Purpose: To investigate the biological effects of radiation damage induced at different depths of a plant seed and to investigate the difference in radiation response between dry seeds and water-imbibed seeds to the same type of radiation.
Materials and methods: Arabidopsis seeds of the wild-type Columbia ecotype were used in our experiments. Dry or water-imbibed Arabidopsis seeds were irradiated with 1.1 MeV, 2.6 MeV or 6.5 MeV protons (H+). For comparison, 30 keV nitrogen ions (N+) were also used to irradiate dry Arabidopsis seeds. The germination and survival rates of the seeds were measured after each irradiation.
Results: After irradiation with 2.6 MeV H+ and 6.5 MeV H+, the fluence-response curves for germination and survival had distinct shoulders and then survival was reduced rapidly with increasing fluence. 2.6 MeV H+ was more effective than 6.5 MeV H+ in inhibiting germination and survival and water-imbibed seeds were more sensitive to the 6.5 MeV H+ irradiation than dry seeds. For 1.1 MeV H+ the germination and survival rates were reduced gradually and an intermediate plateau emerged for germination, which was similar to that observed for survival following 30 keV N+ irradiation. One of the key morphologic malformations, the multi-SAM (shoot apical meristem), was observed both for dry and water-imbibed seeds after all proton irradiations and for the dry seeds after 30 keV N+ irradiation.
Conclusions: Radiation-induced damage produced at different ranges in Arabidopsis seeds results in different fluence-response curves with water-imbibed seeds being more sensitive to proton irradiation than dry seeds. As well as the shoot apical meristem (SAM) being the primary target for irradiation, there exists a secondary target around the SAM that also contributes to the radiation response.