Comparative Characteristics of the Effect of Nickel and Lead on Sorghum bicolor nothosubsp. drummondii f. nigra and Raphanus sativus convar. oleifer Seedlings Formation

Abstract

The increasing levels of toxic metals in the environment are of growing concern. This problem has been significantly exacerbated by the russian military aggression in Ukraine, where military activities have resulted in extensive contamination of terrestrial and aquatic ecosystems. Phytoremediation has attracted increasing attention as an environmentally friendly and cost-effective alternative to chemical methods of soil purification. Our studies were aimed at comparing the characteristics of Sorghum bicolor nothosubsp. drummondii f. nigra (black sorghum) and Raphanus sativus convar. oleifer (oil radish) seedlings in the early stages of growth in the presence of toxic metals. Seeds were germinated at a temperature of 24°C during 7 days on a filter paper in Petri dishes with water solutions of Ni(NO₃)₂ (0, 5, and 10 mg·L^-1 by Ni²⁺) and Pb(NO₃)₂ (100, 200, and 400 mg·L^-1 by Pb²⁺). Shoot and root weight and tolerance indices of seedlings were compared. Shoot tolerance index (TI_sh) of plants of the two species grown in the medium with Ni(II) was close to “1” with a slight predominance of TI_sh of oil radish, however, the root tolerance indices (TI_r) were quite different. The TI_r of black sorghum in the presence of Ni(II) was only 0.221 ±0.037 and 0.102 ±0.015, while TI_r in oil radish was 3-5 times higher. The tolerance index of shoots growing in the medium with Pb(II) was also close to “1” with a slight predominance of TI_sh of oil radish (up to 1.190 ±0.094). The TI_r of black sorghum was equal to 0.682, 0.341 and 0.0, respectively. The TI_r of oil radish was 1.052 ±0.121; 0.723 ±0.105 and 0.356 ±0.079. At the lowest concentration of Pb(II) – 100 mg·L^-1 – it was close to “1”, which indicates moderate resistance of plants to this metal. Thus, according to the TI_r index, oil radish plants turned out to be more resistant than black sorghum plants. Due to the fact that oilseed radish demonstrated higher resistance to both nickel and lead, plants of this species can be considered as potential objects for use in phytoremediation of lands contaminated with these metals, especially if they are present in relatively low concentrations.