Abstract
The antioxidant glutathione (GSH) mitigates adverse physio-metabolic effects and defends against abiotic types of stress, such as cadmium (Cd) stress. However, its function and role in resisting Cd phytotoxicity by leveraging plant antioxidant-scavenging, redox-regulating, and hormone-balancing systems have not been comprehensively and systematically demonstrated in the Cd-hyperaccumulating plant Brassica napus L. cv. Tammi (oilseed rape). In this study, the effects of exogenously applied GSH to the leaves of B. napus seedlings exposed to Cd (10 μM) were investigated. As a result, Cd stress alone significantly inhibited growth and increased the levels of reactive oxygen species (ROS) and the bioaccumulation of Cd in the seedlings compared with those in unstressed controls. Furthermore, Cd stress induced an imbalance in plant stress hormone levels and decreases in endogenous GSH levels and GSH redox ratios, which were correlated with reductions in ascorbate (AsA) and/or nicotinamide adenine dinucleotide phosphate (NADPH) redox states. However, the exogenous application of GSH to Cd-stressed B. napus seedlings reduced Cd-induced ROS levels and enhanced antioxidant-scavenging defenses and redox regulation by both increasing seedling AsA, GSH, and NADPH concentrations and rebalancing stress hormones, thereby enhancing Cd uptake and accumulation. These results demonstrate that GSH improved plant redox status by upregulating the AsA-GSH-NADPH cycle and reestablishing normal hormonal balance. This indicates that exogenously applied GSH can mitigate Cd phytotoxicity in B. napus and possibly other plants. Therefore, GSH can potentially be applied to Cd-polluted soil for plant remediation.
Highlights
Cadmium (Cd), a highly toxic heavy metal, is a non-essential element for all organisms
The analyses of the B. napus plants at the five-leaf stage grown in the presence of 10 μM cadmium for 10 days with or without foliar glutathione treatments (50 and 100 mg kg−1) revealed that the plants that were subjected to cadmium alone exhibited growth inhibition (Table 1)
The exogenous application of GSH to Cd-exposed B. napus plants considerably mitigated the adverse influences of Cd on shoot fresh weight (FW) and dry weight (DW), with the exceptions of root DW and shoot water content (WC) (Table 1)
Summary
Cadmium (Cd), a highly toxic heavy metal, is a non-essential element for all organisms. The mobility of cadmium in soil and water is very high, which makes it possible for the metal to be translocated and accumulated by plants This subsequently leads to the inhibition of normal plant growth, which causes oxidative stress through the production of reactive oxygen species (ROS), such as hydrogen peroxide (H2O2) and superoxide anion radicals (O2–). The overproduction of ROS caused by excessive Cd accumulation destroys cell membranes through lipid peroxidation, and impairs the biosynthesis of essential metabolites required for normal plant growth. This phenomenon severely disrupts normal vital plant functions, such as photosynthesis, respiration, ion uptake, redox homeostasis, and hormone balance (Singh S. et al, 2016)
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