Role of Silicon Counteracting Cadmium Toxicity in Alfalfa


Cadmium (Cd) is one of the most phytotoxic elements causing an agricultural problem and human health hazards. This work investigates whether and how silicon (Si) ameliorates Cd toxicity in Alfalfa. The addition of Si in Cd-stressed plants caused significant improvement in morpho-physiological features as well as total protein and membrane stability, indicating that Si does have critical roles in Cd detoxification in Alfalfa. To get more news about Emeramide, you can visit fandachem.com official website.
Furthermore, Si supplementation in Cd-stressed plants showed a significant decrease in Cd and Fe concentrations in both roots and shoots compared with Cd-stressed plants, revealing that Si-mediated tolerance to Cd stress is associated with Cd inhibition in Alfalfa. Results also showed no significant changes in the expression of two metal chelators [MsPCS1 (phytochelatin synthase) and MsMT2 (metallothionein)] and PC (phytochelatin) accumulation, indicating that there may be no metal sequestration or change in metal sequestration following Si application under Cd stress in Alfalfa. We further performed a targeted study on the effect of Si on Fe uptake mechanisms. We observed the consistent reduction in Fe reductase activity, expression of Fe-related genes [MsIRT1 (Fe transporter), MsNramp1 (metal transporter) and OsFRO1 (ferric chelate reductase] and Fe chelators (citrate and malate) by Si application to Cd stress in roots of Alfalfa. These results support that limiting Fe uptake through the down-regulation of Fe acquisition mechanisms confers Si-mediated alleviation of Cd toxicity in Alfalfa. Finally, an increase of catalase, ascorbate peroxidase, and superoxide dismutase activities along with elevated methionine and proline subjected to Si application might play roles, at least in part, to reduce H2O2 and to provide antioxidant defense against Cd stress in Alfalfa. The study shows evidence of the effect of Si on alleviating Cd toxicity in Alfalfa and can be further extended for phytoremediation of Cd toxicity in plants.

Cadmium (Cd) is a toxic heavy metal affecting plant yield and environment (J?rup and ?kesson, 2009; Naeem et al., 2015). It exhibits varied degrees of phytotoxicity and may replace essential metals or cofactors at enzyme active site causing an imbalance in cellular redox status (Hattab et al., 2014). Furthermore, Cd at toxic level displaces protein structure and disrupts membrane integrity (Rascio and Navarri-Izzo, 2011). Cd is naturally high in agricultural soils due to anthropogenic release and is frequently accumulated in plants. Alfalfa (Medicago sativa L.) is an important forage crop and can accumulate heavy metals, such as Cd, Ni, Cu, Zn, Vn (Peralta-Videa et al., 2002; Yang et al., 2011; Carrasco-Gil et al., 2012). Alfalfa is a source of biological nitrogen fixation, bio-fuel and animal feed. Therefore, reducing Cd bioaccumulation in Alfalfa deserves attention.

Silicon (Si) is an abundant element in the Earth’s crust and plays a role in heavy metal alleviation in plants by different mechanisms (Ma et al., 2008; Greger et al., 2016). One mechanism of Cd detoxification is the reduction of Cd uptake into the plant (Treder and Cieslinski, 2005). Also, Si reduces the translocation of Cd from roots to shoots and thus, prevents the adverse effect of Cd on photosynthetic machinery and grains (Greger and Landberg, 2008; Zhang et al., 2008). However, Cd in high concentration is also trapped in roots through vacuolar sequestrations (Greger et al., 2016), leading to decreased Cd translocation in aerial parts of the plants (Lindberg et al., 2007; Liu et al., 2013). Phytochelatins (PCs) and metallothioneins (MTs) may bind to Cd before transporting the complexes into the vacuole or out of the cell by ATP-binding cassette transporters in few plants (Cobbett, 2000; Jasinski et al., 2003). PCs are formed from glutathione by the induction of PCS1 gene (Semane et al., 2007). Further, MTs are involved in detoxifying cytosolic environment of the cell from Cd toxicity (Cobbett and Goldsbrough, 2002; DalCorso et al., 2010).