Abstract
Lead (Pb) is an important environmental pollutant extremely toxic to plants and other living organisms including humans. To assess Pb phytotoxicity, a pot culture experiment was carried out using two groundnut cultivars (Arachis hypogaea L. cultivar K6 and cultivar K9) on plant growth, ROS levels, lipid peroxidation, and antioxidant metabolism using biochemical, histochemical methods. Plants were grown in pots for 14 days, in the botanic garden, and subjected to Pb-stress (0, 100, 200, 400 and 800 ppm) by adding Pb (NO3)2 solution and further allowed to grow for 10 days. The results showed that cultivar K6 registered lower Pb accumulation than cultivar K9, however, localization of Pb was greater in roots than leaves in both groundnut cultivars. The Pb-stress results in an increase in free radicals (O2•- and H2O2) generation in both groundnut cultivars, but more significantly in cultivar K9 than K6. Pb-stress also caused significant changes in the rate of peroxidation as shown in the levels of malondialdehyde (MDA) content in roots and leaves of both groundnut cultivars. Free proline, ascorbic acid (AsA) and non-protein thiol (NP-SH) contents were increased in cultivar K6 due to Pb-stress, but less in cultivar K9. Pb treated plants showed increased levels of antioxidant enzymes such as superoxide dismutase (SOD), guaiacol peroxidase (GPX), ascorbate peroxidase (APX) glutathione reductase (GR) and glutathione S-transferase (GST). Isozyme band intensities of SOD, GPX and APX were more consistent with the respective changes in antioxidative enzyme activities. These results indicate that cultivar K6 possesses greater tolerance potential for Pb toxicity than cultivar K9.
Highlights
In recent years heavy metal pollution has become one of the serious environmental problems worldwide
The hot spots of soil contamination are located in the regions of large industrial activities, where surrounding agricultural lands are affected by the deposition of heavy metals and agricultural practice, e.g., application of sewage sludges, phosphate fertilizers, liming, irrigation water and pesticides has lead to increased heavy metal concentration in soils [2]
Growth of cultivar K6 was less affected due to Pb treatments compared with cultivar K9
Summary
In recent years heavy metal pollution has become one of the serious environmental problems worldwide. Unlike organic pollutants that can be degradable to harmless small molecules, toxic elements, such as lead, mercury, cadmium, copper and zinc, are immutable by biochemical reactions [1], it is difficult to remediate these metals form the soil and water. The long time persistent nature of some heavy metals, such as Pb and Cd are leading to hazardous accumulation [3], and a huge variation in metal tolerance was observed between different crop plants [4] [5]. Pb is one of the most hazardous pollutants of the environment and Pb pollution in air, water and agricultural soil is an ecological concern due to its extreme impact on human health and environment. Heavy metal induced phytotoxicity or plant tolerant responses to heavy metal stress is a complex phenomenon, involving developmental changes as well as physiological and biochemical mechanisms [5] [7] [8]
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