Effect of gamma rays on nuclear DNA content in different rose genotypes

Abstract:The effect of gamma rays on nuclear DNA content as an index of radiation damage in different genotypes of Rosa hybrida was investigated and the morphological characteristics of the resulting mutants were compared with their own progenitors. The in vitro nodal sections of five rose cultivars ("Apollo", "Maroussia", "Dolce vita", "Black baccara" and "Beauty by ogre") were irradiated by 0, 30, 60 and 90 Gy gamma rays. Nuclear DNA content of the putative mutants and their original plants was estimated by flow cytometry. The results revealed that nuclear DNA content was influenced by different doses of gamma rays. With increasing the dose, nuclear DNA content was decreased significantly. The decrease in nuclear DNA content was directly related to the plant genome size. Reduction in DNA content was greater in genotypes with larger genomes sizes than those with smaller genome sizes. The highest decrease in nuclear DNA content (0.33 pg) was related to the genotype "Black baccara", possessing the biggest genome size (2.49 pg) when irradiated with 90 Gy. The morphological characteristics of the putative mutants (treated with 60 Gy) were noted. The mutants that showed variation in their morphological characteristics did not have a significant difference in nuclear DNA content compared to the control plants. This suggests that changes in nuclear DNA content may not necessarily induce variation in morphological characteristics; moreover mutation may induce changes at the allele level rather than the alterations in the nuclear DNA content which is detectable by flow cytometry.