Cytotoxic and genotoxic alterations as an important biomarker for cadmium and mercury induced stress in plants- A review

Cadmium (Cd) and Mercury (Hg) as toxic metallic mutants can cause various genetic and chromosomal disturbances in plants. Their overproduction due to various domestic and industrial demands leads to excess release to the environment and consequently pose detrimental genotoxic effects on plants and other life forms. They cause phytotoxic problems by directly or indirectly impeding plant growth because of their damage to DNA or cellular components of cell cycle viz. spindle apparatus, DNA polymerases and DNA repair systems. They impose detrimental effects on the genome and cause overproduction of Reactive Oxygen Species (ROS), physiological and/or biochemical irregularities such as decreased membrane stability and photosynthesis, suppression or inhibition of cell division and gene expression. These disruptions lead to impaired growth, delayed development and in long run it results into irreversible cellular damage, programmed cell death. Such conditions ultimately impact overall organismal productivity and survival. Due to their mutagenic or genotoxic effects on plants and other organisms, these are referred to as genotoxins. Genotoxic substances cause DNA damage, which can either be repaired or result in DNA changes. This review is a comprehensive survey on their sources, occurrence, industrial use, exposure impacts and various phytotoxic, cytotoxic and genotoxic effects on plants.