INVOLVEMENT OF PEROXIDASE IN DIFFERENTIAL SENSITIVITY TO GAMMA-RADIATION IN SEEDLINGS OF 2 NICOTIANA SPECIES

Mechanisms underlying differential radiosensitivity were investigated using seeds and seedlings from two Nicotiana species, Nicotiana debney i and Nicotiana tabacum with Co-60 gamma-radiation up to 500 Gy. A con trasting response to radiation was found between the seeds and seedlin gs in these species. Seeds were more radiosensitive in N. debneyi than in N. tabacum with respect to germination rate and subsequent seedlin g development. Conversely, irradiation of seedlings damaged N. tabacum more than N. debneyi, as revealed by inhibition of further seedling g rowth, chlorophyll degradation, and abnormalities in morphology. Subse quent experiments on seedlings revealed that the amount of the radical , OH., generated in irradiated tissues did not appear to differ betwee n the species or with increasing doses of gamma-radiation and that end ogenous antioxidants which might eliminate radicals non-enzymatically were not altered by irradiation in either species irrespective of radi ation doses. Although radiation induced increases in the activities of some antioxidant enzymes (peroxidase, catalase and superoxide dismuta se) and changed isozyme patterns, none of these features could explain the difference in response to radiation in these plants. However, act ivity of peroxidase in non-irradiated tissues was 5-fold higher in N. debneyi than in N. tabacum. It was thus suggested that the difference in response to radiation between these two species was ascribed to the difference in the potential activity of this enzyme to remove toxic h ydrogen peroxide which was produced in irradiated tissues. (C) 1998 El sevier Science Ireland Ltd. All rights reserved.