Effects of Heavy Metal Pollution in Soil on Seed Germination and Seedling Growth of Two Major Oil Crops

  Objective  Possibility of growing sesame(Sesamum indicum) and sunflower(Helianthus annuus) crops on the soil polluted by Pb²⁺, Cd²⁺, Cr⁶⁺, and/or Cu²⁺ was explored in a hydroponic experimentation in laboratory with the respects of seed germination and seedling growth of the plants.

  Method  Seeds of sesame and sunflower cultivars were planted in hydroponics to examine the effects of heavy metals, Pb²⁺ (at 0, 5.0, 10.0, 20.0, 50.0, and 80.0 mg·L⁻¹), Cd²⁺ (at 0, 0.5, 1.0, 5.0, 10.0, and 20.0 mg·L⁻¹), Cr⁶⁺ (at 0, 3.0, 5.0, 8.0, 12.0, and 14.0 mg·L⁻¹) and Cu²⁺ (at 0, 50.0, 100.0, 150.0, 300.0, and 600.0 mg·L⁻¹) on the germination and seedling growth.

  Result  The artificially added heavy metals in the medium decreased the seed germination rates (GR) of both cultivars as the Pb²⁺, Cd²⁺, Cr⁶⁺, and Cu²⁺ concentrations increased. The effect was significantly higher on the sesame seeds than the sunflower seeds (P＜0.01). At lower levels of the heavy metal concentrations, the development and morphogenesis of either seeds were significantly affected. However, as the pollutants were increased in the medium (i.e., Pb²⁺＞80.0 mg·L⁻¹, Cd²⁺＞20.0 mg·L⁻¹, Cr⁶⁺＞14.0 mg·L⁻¹, and Cu²⁺＞600.0 mg·L⁻¹), normal root or bud formation was inhibited on both cultivars. For the growth of the seedlings, the heavy metals exerted greater reductions with Pb²⁺ at 5.0-10.0 mg·L⁻¹, Cd²⁺ at 0.5-20.0 mg·L⁻¹, Cu²⁺ at 50-300.0 mg·L⁻¹, and Cr⁶⁺ at 8.0-12.0 mg·L⁻¹ on the root length of sesame than sunflower plants (P＜0.01), but at 20.0-80.0 mg·L⁻¹ of Pb²⁺ or 14.0 mg·L⁻¹ of Cr⁶, the opposite was observed. For the growth of seedling shoots, Pb²⁺ at 10.0-80.0 mg·L⁻¹, Cd²⁺ at 5.0 mg·L⁻¹, Cu²⁺ at 50.0-100.0 mg·L⁻¹ and 600.0 mg·L⁻¹ or Cr⁶⁺ at 3.0-8.0 mg·L⁻¹ and 14.0 mg·L⁻¹ inhibited it on sunflower more than on sesame, while the opposite was found with Cd²⁺ at 0.5-1.0 mg·L⁻¹ or 10.0-20.0 mg·L⁻¹.

  Conclusion  Heavy metals, Pb²⁺, Cd²⁺, Cr⁶⁺, and/or Cu²⁺, in a hydroponic medium induced greater germination inhibition effect on the sunflower than the sesame seeds. The growth of roots and buds of sesame seedlings appeared more tolerant to Pb²⁺ at 20.0-80.0 mg·L⁻¹, Cr⁶⁺ at 14.0 mg·L⁻¹, and Cu²⁺ at 150.0-300.0 mg·L⁻¹ than that of the sunflower counterparts, while the sunflower seedlings were more tolerant to Cd²⁺ at 0.5-1.0 mg·L⁻¹ and 10.0-20.0 mg·L⁻¹.