Silicon Alleviates Cadmium Toxicity in Triticum aestivum L. Plants by Modulating Antioxidants, Nutrient Uptake, and Gene Expression

SILICON (Si) is beneficial for plant growth and has the potential to alleviate the deleterious effects of heavy metals in plants grown on contaminated soils. This study aimed to evaluate the adaptive mechanisms induced by Si application (1mM sodium meta-silicate, Na2O3 Si.9H(2)Ox) in Triticum aestivum L. plants subjected to cadmium (Cd) stress (100 and 200 mu M CdSO4). Under Cd stress, Si application significantly increased plant biomass, relative water content, nutrient uptake, and allocation as well as Si content while it decreased Cd accumulation compared to Cd-stressed plants. Si application also induced lignin content, mainly in roots, in the presence or absence of Cd in comparison to controls. Cd stress significantly increased the accumulation of oxalate, malate and citrate contents in the roots in comparison to control, whereas Si supplementation increased malate, and citrate in shoots. Additionally, Cd-induced oxidative stress designated by the increment of malondialdehyde, H2O2 contents and electrolyte leakage was diminished upon Si application. Concomitantly, Cd-stress markedly enhanced glutathione reductase (GR), glutathione peroxidase (GSHPx), and ascorbate peroxidase (APx) while GSH/GSSG and A SA/DHASA ratios decreased. Si application significantly induced all tested antioxidant enzymes and increased GSH/ GSSG and ASA/DHASA ratios. Interestingly, low-affinity Cd transporter (LCT1), ATPase/heavy metal transporter (HMA2), and phytochelatine synthase (PCs) genes expression decreased in the shoots and roots of Si+ Cd-treated plants, while that of Si transporter (Si1) markedly increased, which may contribute to Cd uptake reduction and increased Si content. Taken together, the results highlight the role of Si in alleviating the adverse effect of Cd on wheat plants.