Abstract
Among heavy metals, cadmium is considered one of the most toxic and dangerous environmental factors, contributing to stress by disturbing the delicate balance between production and scavenging of reactive oxygen species (ROS). To explore possible relationships and linkages between Cd(II)-induced oxidative stress and the consequent damage at the genomic level (followed by DNA replication stress), root apical meristem (RAM) cells in broad bean (V. faba) seedlings exposed to CdCl2 treatment and to post-cadmium recovery water incubations were tested with respect to H2O2 production, DNA double-strand breaks (γ-phosphorylation of H2AX histones), chromatin morphology, histone H3S10 phosphorylation on serine (a marker of chromatin condensation), mitotic activity, and EdU staining (to quantify cells typical of different stages of nuclear DNA replication). In order to evaluate Cd(II)-mediated epigenetic changes involved in transcription and in the assembly of nucleosomes during the S-phase of the cell cycle, the acetylation of histone H3 on lysine 5 (H3K56Ac) was investigated by immunofluorescence. Cellular responses to cadmium (II) toxicity seem to be composed of a series of interlinked biochemical reactions, which, via generation of ROS and DNA damage-induced replication stress, ultimately activate signal factors engaged in cell cycle control pathways, DNA repair systems, and epigenetic adaptations.
Highlights
Morphogenetic processes in plants are determined by cell divisions in the primary shoot and root apical meristems (SAMs and RAMs, respectively) and in the secondary meristems, the cambia
reactive oxygen species (ROS) are believed to be involved in signal transduction pathways; the overproduction of ROS and disruption of redox homeostasis brings about interactions with all kinds of organic molecules [36]
Cadmium (Cd(II) ions), among other heavy metals, has been considered a dangerous stress factor that contributes to the disturbance of the delicate balance between ROS production and scavenging
Summary
Morphogenetic processes in plants are determined by cell divisions in the primary shoot and root apical meristems (SAMs and RAMs, respectively) and in the secondary (lateral) meristems, the cambia All these regions, comprising cell populations characterized by a high mitotic activity, are exposed to and endangered by a variety of stress conditions, including those resulting from environmental contamination with heavy metals. By using primary root meristems of Vicia faba as an experimental model, our present study was aimed at finding possible relationships and linkages between cadmium (the primary cause of observable effects) and two types of consequent cadmium-induced secondary stress conditions, i.e., oxidative stress, which by reactive oxygen species (ROS) may play an important part in producing disorder at the genomic DNA level, leading to replication stress. In order to evaluate cadmium-induced epigenetic changes involved in the assembly of nucleosomes during DNA replication and repair processes, localized in the promoter sequences of active genes (to enhance transcriptional processes), acetylation of histone H4 on Lys 5 (H4K5Ac) was investigated by immunofluorescence
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