engleski

Peroxidase activity, lipid peroxidation and proline content in lettuce and radish leaves under heavy metal stress

Lettuce (Lactuca sativa L.) and radish (Raphanus sativus L.) were grown in nutrient solution in controlled conditions till 5-6 leaf stage and exposed to 500 µ ; M Cu or Pb or 48 h. The heavy metal stress and plant response were defined by peroxidase specific activity (GPOX), lipid peroxidation level (TBARS) and free proline content in leaves. The GPOX activity was twofold higher in radish leaves, both in control and in heavy metal treated plants. In lettuce leaves it was under significant influence of heavy metal treatment as well as cultivar x heavy metal treatment interaction (p≤ 0.01). In radish leaves, the cultivar showed higher influence than excess Pb or Cu in nutrient solution. Cu treatment induced significantly higher enzyme activity while Pb treated plants of both species did not differ from control plants. TBARS level was not influenced by metal toxicity in lettuce indicating successful antioxidant response to short exposure to heavy metal stress, while in radish leaves it was 72% higher in Cu treatment and 36% higher in Pb treatment as compared to control plants. The tested cultivars showed distinct differences in free proline content. The excess Cu led to the increment in free proline and treatment with Pb resulted in much more free proline in lettuce leaves. The accumulation of proline in radish leaves was also influenced by cultivar, heavy metal treatment and their interaction, showing much lower levels compared to lettuce. Proline in radish leaves was similar in Cu and Pb treated plants. Estimated TBARS levels, although not directly related to heavy metal stress, were negatively correlated to leaf fresh weight (r=-0.81**) in general. Higher TBARS was followed by higher GPOX activity (r=0.735**) and the accumulation of free proline resulted with lower TBARS (r=-0.783**). Finally, the higher leaf proline concentration lead to higher leaf fresh weight per plant (r=0.663**). This investigation implies that both vegetable species could suppress the oxidative stress under short exposure to excess Cu or Pb, but the mechanism of defence was different. Lettuce responded to the applied heavy metals by proline accumulation. With lower leaf fresh weight compared to lettuce, radish showed higher lipid peroxidation level under excess Cu or Pb and had higher peroxidase activity. A further analysis of other kinds of antioxidative response is required for better comprehension of heavy metal stress in shallow- rooted vegetables that are often grown in garden soils, feasible polluted through many years exposure to traffic (Pb) and application of Cu-based fungicides.

heavy metal stress ; peroxidase ; lipid peroxidation ; proline

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