Abstract
Environmental contamination with arsenic (As) is a global environmental, agricultural and health issue due to the highly toxic and carcinogenic nature of As. Exposure of plants to As, even at very low concentration, can cause many morphological, physiological, and biochemical changes. The recent research on As in the soil-plant system indicates that As toxicity to plants varies with its speciation in plants (e.g., arsenite, As(III); arsenate, As(V)), with the type of plant species, and with other soil factors controlling As accumulation in plants. Various plant species have different mechanisms of As(III) or As(V) uptake, toxicity, and detoxification. This review briefly describes the sources and global extent of As contamination and As speciation in soil. We discuss different mechanisms responsible for As(III) and As(V) uptake, toxicity, and detoxification in plants, at physiological, biochemical, and molecular levels. This review highlights the importance of the As-induced generation of reactive oxygen species (ROS), as well as their damaging impacts on plants at biochemical, genetic, and molecular levels. The role of different enzymatic (superoxide dismutase, catalase, glutathione reductase, and ascorbate peroxidase) and non-enzymatic (salicylic acid, proline, phytochelatins, glutathione, nitric oxide, and phosphorous) substances under As(III/V) stress have been delineated via conceptual models showing As translocation and toxicity pathways in plant species. Significantly, this review addresses the current, albeit partially understood, emerging aspects on (i) As-induced physiological, biochemical, and genotoxic mechanisms and responses in plants and (ii) the roles of different molecules in modulation of As-induced toxicities in plants. We also provide insight on some important research gaps that need to be filled to advance our scientific understanding in this area of research on As in soil-plant systems.
Highlights
Contamination of air, soil, and water resources with potentially toxic elements (PTEs) is a global environmental issue [1,2]
Livanos et al [216] reported that several root cells of a mutant Arabidopsis thaliana (RHD2), which lacks the RHD2/AtRBOHC protein function, exhibited aberrations, compared to those induced by low reactive oxygen species (ROS) levels
Singh et al [196] observed higher accumulation of MDA in Pteris ensiformis than that of Pteris vittata and suggested that Pteris vittata was able to maintain homeostatic control over photosynthetic light reactions under As stress. This entails that Pteris vittata could not produce more ROSs and as such resulted in a low amount of MDA generation
Summary
Contamination of air, soil, and water resources with potentially toxic elements (PTEs) is a global environmental issue [1,2]. In the soil and water environments, As can exist in four different oxidation states: As(-III), As(0), As(III), or As(V) [16] Both organic (e.g., monomethyl arsonic acid, arsenobetaine, and arsenosugars) and inorganic species of As are present, the latter being more toxic and mobile than organic As species. Among non-enzyme antioxidants, proline is a well-known osmoprotectant that is largely accumulated in plants under As stress [6,32,47] It serves as a cell wall plasticizer and helps maintain a minimum level of hydration needed for the normal functioning of cell and protects plants against ROS-mediated damages [22,32,48,49]. The protective role of the exogenous supplies of proline, SA, NO, and Pi for plants under As stress are addressed
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