Abstract
The alleviative effects of silicon (Si) on cadmium (Cd) toxicity were investigated in cucumber (Cucumis sativus L.) and tomato (Solanum lycopersicum L.) grown hydroponically. The growth of both plant species was inhibited by 100 μM Cd, but Si application counteracted the adverse effects on growth. Si application significantly decreased the Cd concentrations in shoots of both species and roots of cucumber. The root-to-shoot transport of Cd was depressed by added Si in tomato whereas it was increased by added Si in cucumber. The total content of organic acids was decreased in tomato leaves but increased in cucumber roots and leaves by Si application under Cd stress. Si application also increased the cell wall polysaccharide levels in the roots of both species under Cd toxicity. Si-mediated changes in levels of organic acids and cell wall polysaccharides might contribute to the differences in Cd transport in the two species. In addition, Si application also mitigated Cd-induced oxidative damage in both species. The results indicate that there were different mechanisms for Si-mediated decrease in shoot Cd accumulation: in tomato, Si supply decreased root-to-shoot Cd transport; whereas in cucumber, Si supply reduced the Cd uptake by roots. It is suggested that Si-mediated Cd tolerance is associated with different physiological responses in tomato and cucumber plants.
Highlights
In recent decades, extensive industrial and anthropogenic activities have caused serious heavy metal pollution
Cd does not participate in Fenton-type reaction directly, it can indirectly induce production of reactive oxygen species (ROS) such as superoxide radical (O2−), hydrogen peroxide (H2O2), and hydroxyl radical (OH) (Stohs and Bagchi, 1995; Gonçalves et al, 2007)
Nitroblue tetrazolium (NBT) method was used for determination of superoxide dismutase (SOD) activity and one unit SOD activity was defined as the amount of enzyme required to cause a 50% inhibition of the rate of NBT reduction
Summary
Extensive industrial and anthropogenic activities have caused serious heavy metal pollution. As a highly mobile and toxic element, cadmium (Cd) pollution is increasingly of concern. Cd toxicity can disturb morphological, biochemical and ultrastructural functions in plants (Ali et al, 2013, 2014). Cd does not participate in Fenton-type reaction directly, it can indirectly induce production of reactive oxygen species (ROS) such as superoxide radical (O2−), hydrogen peroxide (H2O2), and hydroxyl radical (OH) (Stohs and Bagchi, 1995; Gonçalves et al, 2007). Excessive ROS production can disturb the balance of nutritional status and induce oxidative damage. Cd accumulation in crops and vegetables that exceeds the safety threshold will endanger human health via food chain (Aery and Rana, 2003; López-Millán et al, 2009)
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