Effects of polycyclic aromatic hydrocarbons stress on growth and physiological characteristics of Brassica parachinensis

Objective  To determine the effects of polycyclic aromatic hydrocarbons (PAHs) stress on the growth of Chinese flowering cabbage (Brassica parachinensis), and explore the physiological toxicity of PAHs.

Method  The PAHs solution mixing naphthalene, phenanthrene, fluoranthene, benzopyrene and indenopyrene was applied to soil to stress the growth of B. parachinensis. The changes of malondialdehyde(MDA), H₂O₂ and proline contents and antioxidase activites in leaves of B. parachinensis were analyzed on the 10th, 17th, and 24th day after planting, and the growth was measured on the 24th day after planting.

Result  The plant height of B. parachinensis was increased by PAHs treatments, and it was highest under 10.0 mg·kg^–1 PAHs treatment. The treatments of 0.4 and 0.8 mg·kg^–1 PAHs had little effects on stem diameter of B. parachinensis, but had some promotions on individual plant fresh weight and root fresh weight. The stem diameter, individual plant fresh weight and root fresh weight of B. parachinensis were decreased by 2.0, 5.0 and 10.0 mg·kg^–1 PAHs treatments for different degrees. The contents of MDA, H₂O₂ and proline in leaves of B. parachinensis increased with the stress time and PAHs content increasing. With the PAHs content increasing, the activity of superoxide dismutase(SOD) increased, and the activities of peroxidase(POD), catalase(CAT) and ascorbic acid peroxidase(APX) increased firstly and then decreased.

Conclusion  Stress from low content of PAHs has little effect on the growth of B. parachinensis, while stress from high content of PAHs can inhibit plant normal growth as it decreases stem diameter, individual plant fresh weight and root fresh weight and also causes earlier blooming. B. parachinensis could alleviate the disadvantageous effects from increasing contents of H₂O₂ and MDA under PAHs stress by increasing proline content and antioxidant enzyme activities.