Mitigation of Cadmium Toxicity in Edible Rape ( Brassica Rapa L.) by Combined Application of Chitosan and Silicon

Cadmium (Cd) is a heavy metal that is highly toxic to humans and plants. Adding chitosan (CTS) or silicon (Si) can reduce the uptake of Cd and mitigate Cd toxicity in plants, but the joint effects of CTS and Si on alleviating Cd toxicity remain unclear. Therefore, this study evaluated the effects of CTS alone, Si alone, and their mixture on the growth, biochemical parameters, and Cd uptake by Cd-treated edible rape plants under greenhouse conditions. The results showed that adding CTS only or Si only could significantly minimize the accumulation of Cd and alleviate Cd toxicity in edible rape, and a strong joint effect of adding both CTS and Si was found. The combined application of CTS and Si significantly increased growth and the leaf chlorophyll contents, decreased the malondialdehyde contents, and reduced the accumulation of Cd in the shoots of rape plants. The simultaneous application of CTS and Si also increased the antioxidant enzyme activities in the shoots and the proportion of Cd in the root cell walls by 40.4%. Furthermore, the Cd translocation factor was 66.4% lower under the combined CTS and Si treatment compared with treatment using only Cd. These results indicated that CTS and Si had a strong effect on alleviating Cd toxicity by enhancing the oxidative stress response and suppressing the uptake and transport of Cd.