Abstract
The sensitivity of different plant species to mutagenic agents is related to the DNA content and organization of the chromatin, which have been described in ABCW and bodyguard hypotheses, respectively. Plant species that have B chromosomes are good models for the study of these hypotheses. This study presents an analysis of the correlation between the occurrence of B chromosomes and the DNA damage that is induced by the chemical mutagen, maleic hydrazide (MH), in Crepis capillaris plants using comet assay. The presence of B chromosomes has a detectable impact on the level of DNA damage. The level of DNA damage after MH treatment was correlated with the number of B chromosomes and it was observed that it increased significantly in plants with 3B chromosomes. We did not find evidence of the protective role from chemical mutagens of the constitutive heterochromatin for euchromatin in relation to DNA damage. The DNA damage involving the 25S rDNA sequences was analyzed using the comet-FISH technique. Fragmentation within or near the 25S rDNA involved the loci on the A and B chromosomes. The presence of B chromosomes in C. capillaris cells had an influence on the level of DNA damage that involves the 25S rDNA region.
Highlights
Numerous factors determine the genetic effect that is observed after mutagenic treatment, including the ability of mutagens to penetrate the tissue, cells and nucleus; the concentration of the mutagen and the treatment time [1]
These results indicate the higher susceptibility of the C. capillaris plants to the chemical mutagen, maleic hydrazide (MH), when B chromosomes are present
The presence of supernumerary chromosomes in C. capillaris is associated with increase in DNA damage induced by the chemical mutagen, MH
Summary
Numerous factors determine the genetic effect that is observed after mutagenic treatment, including the ability of mutagens to penetrate the tissue, cells and nucleus; the concentration of the mutagen and the treatment time [1]. The somatic and genetic effects differ in different plant species and as well as within different varieties. The sensitivity of different plant species to mutagenic agents appears to be related to their nuclear volume and DNA content [2]. The amount and type of chromatin in the nucleus may affect the induced mutations rates. The bodyguard hypothesis proposes that a constitutive heterochromatin may protect euchromatin from chemical mutagens [3]. Heterochromatin localizes during interphase near the nuclear membrane which can absorb environmental stimuli more than euchromatin and it may protect the DNA from being mutated. The ABCW hypothesis states that the mutation rate per locus is proportional to the DNA content of a species [4], [5]
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