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Mohammad Esmaeil Amiri

Zahra Aghcheh Kahrizi,  Maryam Jafarkhani Kermani, hammad Amiri 2  
   Effect of gamma rays on nuclear DNA content in different rose genotypes

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.    



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