Nitric Oxide Supplementation Can Improve the Phytoremediation Potential of Ricinus communis by Regulating the Antioxidant Functioning, Redox Components, and Metal Accumulation

Potential of exogenously applied nitric oxide (NO; 50 and 100 μM) in improving the tolerance of Ricinus communis to nickel (Ni), zinc (Zn), and arsenic (As) stress. Applied NO alleviated the decline in growth, chlorophyll and carotenoids, glutamate 1-semialdehyde, and δ-amino levulinic acid, and the activity of δ-amino levulinic acid dehydratase and Rubisco. The oxidative stress parameters, like hydrogen peroxide, lipid peroxidation, and the activity of chlorophyllase, protease, and NADPH oxidase, were substantially reduced in NO-treated plants. NO promoted osmolyte accumulation and enhanced the antioxidant enzyme activity and the levels of reduced glutathione and cysteine, facilitating the radical scavenging and redox homeostasis. Importantly, NO reduced Ni, Zn, and As accumulation and mitigated the metal-induced decline in essential mineral elements. These results suggest that NO application improves phytostabilization of heavy metals by Ricinus communis, therefore contributing to its improved tolerance to grow in Ni, Zn, and As contaminated soils.