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Title: SEM Studies of Leaf Surface Structure Changes Due to Lead Toxicity in Hypericum perforatum L
Authors: Sima Ghelich; Fatemeh Zarinkamar
Aff: Faculty of biological Sciences, Tarbiat Modares University, Tehran, Iran
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Keywords: Pb; Stomata; Epicuticular Waxes; Hypericum perforatum L
Abstract:In the recent years, human activities such industry and agriculture promote heavy metal release into the environment. Lead (Pb) is the most common heavy metal contaminant in the environment. It is a nonessential element in metabolic processes and may be toxic or lethal to organisms even when absorbed in small amounts. Hypericum perforatum L is a medicinal plant is mainly due to the presence of naphtodianthrones such as hypericin and pseudohypericin. The present study was undertaken to determine the accumulation the lead in shoots of H. perforatum L. and itís effects on leaf surface structure changes in mature plants treated with contaminated soil in 7 treatments (75, 150, 300, 600, 800, 1000, 1500 mg/kg Pb in soil) and 3 treatments by foliar spray (0.724, 1.44, 2.9 mM Pb) with 3 repeat in per treatment for 14 days. Results indicated the Maximum observed Pb content in shoot parts was at the two treatments 600 and 1500 mg/kg Pb in soil and in in foliar spray maximum Pb content observed at 0.724 mM Pb and the deareased to 2.9 mM Pb but all treatments have significant differenc with control plants. The analysis of scanning electron micrographs of the leaf surface of H. perforatum grown on polluted soil showed an increase in the size of guard cells In both adaxial and abaxial surfaces with increasing Pb in soil, decrease in size of stomata aperture and closure of stomata in 600 and 1500 mg/kg Pb in soil, and alteration in structure and deposition of epicuticular waxes. In foliar spray treatments In both adaxial and abaxial surfaces size of stomata aperture decreased than control leaves but not completely closed. Also Size of guard cells in treated leaves decreased compared to the control leaves. Also Studies of leaf surface by SEM indicated that affected epicuticular waxes by Pb concentrations in foliar spray treatments. the epicuticular wax deposition in control leaf in both adaxial and abaxial surfaces was less than Pb treated leaves and it increased with increase of Pb concentration.