Effect of Low-Dose Nano Titanium Dioxide Intervention on Cd Uptake and Stress Enzymes Activity in Cd-Stressed Cowpea [Vigna unguiculata (L.) Walp] Plants.

Cadmium contamination of agricultural soils is a serious problem due to its toxic effects on health and yield of crop plants. This study investigates the potential of low-dose nano-TiO2 as soil nanoremediation on Cd toxicity in cowpea plants. To achieve this goal, cowpea seeds were germinated on Cd-spiked soils at 10 mg/kg for 14 days and later augmented with 100 mg nTiO2/kg (nTiO2-50 nm and bTiO2-68 nm, respectively). The results showed that chlorophylls were not altered by nano-TiO2 intervention. Cadmium partitioning in roots and leaves was reduced by the applied nano-TiO2 but significantly higher than control. Ascorbate peroxidase and catalase activities in roots and leaves were promoted by nano-TiO2 intervention compared to control and sole Cd, respectively. However, magnitudes of activity of enzyme activities were higher in nTiO2 compared to bTiO2 treatments. The enhanced enzymes activity led to reduced malonaldehyde content in plant tissues. The study concludes that soil application of nano-TiO2 could be a green alternative to ameliorate soil Cd toxicity in cowpea plants.

Effects of manufactured nano-copper on copper uptake, bioaccumulation and enzyme activities in cowpea grown on soil substrate.

Increased use of nanoparticles-based products in agriculture portends important implications for agriculture. Therefore, the impact of nano-copper particles (<25 nm and 60-80 nm) on Cu uptake, bioaccumulation (roots, leaves and seeds), activity of ascorbate peroxidase (APX), catalase (CAT), superoxide dismutase (SOD), glutathione reductase (GR), and lipid peroxidation in leaves and roots of Vigna unguiculata (cowpea) was studied. Plants were exposed to four levels (0, 125, 500 and 1000 mg/kg) of 25 nm or 60-80 nm nano-Cu for 65 days. Results indicated significant (P<.05) uptake of Cu at all nano-Cu levels compared to control, and bioaccumulation increased in seeds by at least 250%. Response of antioxidant enzymes to both nano-Cu types was concentration-dependent. Activity of APX and GR was enhanced in leaves and roots in response to both nano-Cu treatments in similar patterns compared to control. Both nano-Cu increased CAT activity in roots while SOD activity reduced in both leaves and roots. This shows that response of antioxidant enzymes to nano-Cu toxicity was organ-specific in cowpea. Malondialdehyde, a measure of lipid peroxidation, increased at 500 -1000 mg/kg of 25 nm nano-Cu in leaves by average of 8.4%, and 60-80 nm nano-Cu in root by 52.8%, showing particle-size and organ-dependent toxicity of nano-Cu. In conclusion, exposure of cowpea to nano-Cu treatments increased both the uptake and bioaccumulation of Cu, and also promoted the activity of APX and GR in root and leaf tissues of cowpea. Therefore, APX- and GR-activity level could be a useful predictive biomarker of nano-Cu toxicity in cowpea.