Agriculture Reference
In-Depth Information
from the counterparts located in the cytosol and in other subcellular compartments
(Go and Jones
2010
). This is the case of the protein 1-Cys peroxiredoxin (1-Cys
Prx), activated under oxidative stress conditions in the nucleus of wheat (
Triticum
aestivum
L.) seed cells following reduction mediated by the NADPH thioredoxin
reductase/thioredoxin h (NTR/Trx h) system (Pulido et al.
2009
).
Recently, Vanderauwera et al. (
2011
) reported that the extranuclear protection of
chromosomal DNA in
Arabidopsis thaliana
plants involves the coordinated action
of ROS-scavenging pathways localized both in the cytosol and peroxisomes. The
antioxidant enzymes catalase (CAT2) and ascorbate peroxidase (APX) were found
to play a key role, mediated by a WEE1 kinase-dependent cell-cycle checkpoint, in
preserving the plant genome integrity (Vanderauwera et al.
2011
).
The emerging picture highlights the complexity of the interactions, involving the
nucleus and the other subcellular compartments, which are an integral part of the
cell response to genotoxic stress.
3 Genotoxic Adaptation
Genotoxic adaptation represents an interesting aspect of the plant response to ad-
verse environmental conditions. It has been reported that exposure to minimal stress
levels causes a limited cellular damage which triggers the so-called “adaptive re-
sponse” (AR), responsible for increased resistance to high levels of the same stress
or other stresses (Dimova et al.
2008
). The term “genotoxic adaptation” is used to
address the response of cells exposed to low doses of genotoxic agents and the sub-
sequent induction of stress tolerance.
The AR involves activation of signaling pathways and up-regulation of gene ex-
pression, which contribute to multiple cell defense mechanisms such as ROS scav-
enging, DNA repair and production of antioxidant compounds. Thanks to these
mechanisms, the “primed” cells can better withstand genotoxic stress. Till date, con-
trasting findings have been reported concerning the involvement of DNA repair genes
in AR. It has been suggested that the up-regulation of DNA repair genes might be es-
sential; however the experimental results have not always supported this hypothesis.
Clastogenic adaptation, defined as the protection of plant cells against chroma-
tid aberrations induced by genotoxic agents, can be obtained by pre-treating cells
with non-effective low doses of the same agents in order to elicit a protective re-
sponse. It has been reported that clastogenic adaptation correlates with removal of
O
6
-methylguanine from DNA after pre-treatments (Baranczewski et al.
1997
). The
study carried out by Angelis et al. (
2000
) in
Vicia faba
root tip nuclei pretreated
with alkylating mutagens, demonstrated that adaptation takes place soon after the
pre-treatment. The level of AP sites, measured using the comet assay, revealed a
significant reduction in the number of these lesions, which were preferentially re-
moved while the majority of DNA damage was not affected. This finding suggests
the possible involvement of AP glycosylases, typical components of the base exci-
sion repair (BER) pathway, in genotoxic adaptation.
