Involvement of peroxidase in differential sensitivity to γ-radiation in seedlings of two Nicotiana species

Mechanisms underlying differential radiosensitivity were investigated using seeds and seedlings from two Nicotiana species, Nicotiana debneyi and Nicotiana tabacum with Co-60 gamma-radiation up to 500 Gy. A contrasting response to radiation was found between the seeds and seedlings in these species. Seeds were more radiosensitive in N. debneyi than in N. tabacum with respect to germination rate and subsequent seedling development. Conversely, irradiation of seedlings damaged N. tabacum more than N. debneyi, as revealed by inhibition of further seedling growth, chlorophyll degradation, and abnormalities in morphology. Subsequent experiments on seedlings revealed that the amount of the radical, OH., generated in irradiated tissues did not appear to differ between the species or with increasing doses of gamma-radiation and that endogenous antioxidants which might eliminate radicals non-enzymatically were not altered by irradiation in either species irrespective of radiation doses. Although radiation induced increases in the activities of some antioxidant enzymes (peroxidase, catalase and superoxide dismutase) and changed isozyme patterns, none of these features could explain the difference in response to radiation in these plants. However, activity 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 hydrogen peroxide which was produced in irradiated tissues. (C) 1998 Elsevier Science Ireland Ltd. All rights reserved.