Abstract
The effect of four soil-applied sulfur (100 mg S kg−1 soil (100S) and 200 mg S kg−1 soil (200S)) in different sources (elemental S, ammonium sulfate, gypsum or magnesium sulfate) in protecting mustard (Brassica juncea L. (Czern & Coss.)) from cadmium effects was studied. Based on the observed reduction in growth and photosynthesis in plants subjected to 100 and 200 mg Cd kg−1 soil, B. juncea cv. Giriraj was selected as the most Cd-tolerant among five cultivars (namely, Giriraj, RH-0749, Pusa Agrani, RH-406, and Pusa Tarak). Sulfur applied to soil mitigated the negative impact of Cd on sulfur assimilation, cell viability, and photosynthetic functions, with a lower lipid peroxidation, electrolyte leakage, and contents of reactive oxygen species (ROS: hydrogen peroxide, H2O2, and superoxide anion, O2•−). Generally, added S caused higher activity of antioxidant enzymes (ascorbate peroxidase, catalase and superoxide dismutase), contents of ascorbate (AsA) and reduced glutathione (GSH); increases in the activities of their regenerating enzymes (dehydroascorbate reductase and glutathione reductase); as well as rises in S assimilation, biosynthesis of non-protein thiols (NPTs), and phytochelatins (PCs). Compared to the other S-sources tested, elemental S more prominently protected B. juncea cv. Giriraj against Cd-impacts by minimizing Cd-accumulation and its root-to-shoot translocation; decreasing cellular ROS and membrane damage, and improving Cd-chelation (NPTs and PCs), so strengthening the defense machinery against Cd. The results suggest the use of elemental S for favoring the growth and development of cultivated plants also in Cd-contaminated agricultural soils.
Highlights
The issues concerning the continuous accumulation of metals in agricultural soils because of the anthropogenic activities have been widely reviewed and discussed over the past 30 years [1,2,3]
To assess the S-requirement of the crop, we evaluated the effects of two S levels (100S and 200 mg S kg−1 soil (200S)) from four S sources on growth and photosynthetic paramet7eorfs2,3and S-assimilation (Table 3 and Figure 1)
200S treatment was more effective than 100 mg S kg−1 soil (100S) in counteracting Cd stress in B. juncea
Summary
The issues concerning the continuous accumulation of metals in agricultural soils because of the anthropogenic activities have been widely reviewed and discussed over the past 30 years [1,2,3]. Cadmium (Cd), a hazardous heavy metal pollutant, has wide distribution, short half-life, and higher solubility in water, without a known biological function in plants. Cadmium enters the human food chain by getting accumulated in agricultural crops, causing severe threats to human and animal health [4]. The presence of Cd potentially stimulates the major plant enzymes, like NADPH oxidases, whose activity produce reactive oxygen species (ROS), such as singlet oxygen (1O2), hydroxyl radicles (OH), superoxide anion (O2−), and hydrogen peroxide (H2O2). These, in turn, cause membrane lipid peroxidation, and disturb redox homeostasis [5,6]. To counter Cd-induced phytotoxicity and excessive ROS, plants employ a series of defense mechanisms, comprising enzymatic antioxidants (such as superoxide dismutase, SOD; ascorbate peroxidase, APX; catalase, CAT; and glutathione reductase, GR), non-enzymatic antioxidants (such as ascorbate, AsA; glutathione, GSH), and non-protein thiols (NPTs)
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