Mitigation of lead toxicity through nano-particles in Basella alba – A solution for production of healthy vegetables in contaminated media

Abstract

Among heavy metal contaminants in soil, lead (Pb) is a potentially toxic element to plant growth and humans due to non-degradable nature. Nowadays, concentration of Pb in cultivable soil has increased tremendously due to different anthropogenic activities such as untreated sewage water, industrialization etc. Present study explored the role of ZnO and Fe2O3 nanoparticles (NPs) in alleviating stress symptoms caused by lead (Pb) exposure in Basella alba during seed germination and seedling growth. After preliminary study, 15 different treatment combinations of seed priming with two NPs (ZnNPs and FeNPs at 0 & 200 mg/L) and Pb (0, 4, 8, 15, 20 mM), were chosen to investigate the effect of the NPs in Pb contaminated media. Pb stress (0 to 20 mM) was found to reduce seed germination (72.8 %) and seedling growth, particularly root growth (92 %). Under Pb stress conditions, however, seed priming with ZnNPs (200 mg/L) and FeNPs (200 mg/L) resulted in increase in seed germination and root length. The content of Pb in seedling decreased by 20.2–33.7% and 24.6–32.6%, respectively, in Pb + ZnNPs and Pb + FeNPs treatments. Increasing Pb stress resulted in increased reactive oxygen species (ROS) generation (H2O2 content), and lipid peroxidation (MDA content) compared to non-Pb stressed seedlings. These ROS were scavenged however, by increased production of SOD, CAT, POX and proline content in the Pb + ZnNPs and Pb + FeNPs treatments. To summarise, seed priming with NPs has the potential to alleviate Pb toxicity by (1) reduction in Pb uptake (2) reduction in ROS and lipid peroxidation (3) increase in proline (4) activation of antioxidant enzymes. It is recommended that seed priming with either of the NPs could be used in the remediation of Pb contaminated media for healthy vegetable production.