Alleviation of Cadmium Toxicity by Nano-silicon Dioxide in Momordica charantia L. Seedlings

Heavy metal cadmium (Cd) is a toxic element which poses a great threat to environment and human health; nanomaterials are emerging materials with great potential in promoting plant growth and improving crop stress resistance. The main purpose of the current study was to investigate the mitigation effects of nano-silicon dioxide (nSiO2) on Cd toxicity to Momordica charantia L. (bitter gourd) seedlings. We conducted hydroponic experiments on bitter gourd seedlings grown under control and Cd toxicity (50 μmol L−1) and Cd combined with 10 (nSi10) and 30 (nSi30) mg L−1 of Si in form of nSiO2 soliquid applied on the 5th day after transplanting. Exogenous application of nSiO2 increased Cd stress tolerance in bitter gourd by enhancing chlorophyll content, photosynthetic rate (Pn), transpiration rate (Tr), and stomatal conductance (Gs) and promoted certain antioxidant response by increasing leaf/root SOD, root APX, peroxidase (POD), and catalase (CAT) activities and depressed flavonoids and soluble sugar contents under Cd stress. Furthermore, Cd-stressed plants displayed an upper level of malondialdehyde (MDA) (1.71-, 1.45-, and 1.53-fold in the leaves, stems, and roots, respectively), while nSiO2 improved membranous integrity through abating MDA contents in all tissues. Additionally, nSiO2 improved Cd-treated plant growth (plant height, leaf area, plant dry weight (DW), plant fresh weight (FW)), diminished Cd concentration in all plant tissues, and application of 30 mg L−1 nSiO2 (Cd+nSi30) reduced stem and root Cd concentration by 7.3%, and 33.8%, respectively, as compared with respective Cd-exposed alone. The study suggested that the use of nSiO2 may be a tool for reducing the Cd toxicity in bitter gourd and declining its concentration in plants. Cd toxicity reduced growth and productivity of bitter gourd seedlings. However, application of nSiO2 was effective in enhancing the physiological performance, photosynthesis, and plant growth of bitter gourd under Cd stress condition. Therefore, nSiO2 may, in future, find value as a potential plant growth stimulant under Cd stress.