Lead Accumulation In Roots Research Articles

The effects of lead on the gaseous exchange and photosynthetic carbon metabolism of pea seedlings

Roots of whole 3 week-old pea seedlings (Pisum sativum L.) var. "Bordi" were immersed for 24 h in solutions of lead chloride at Pb copcentrations of 200, 400, 800,12000 mg dm3. Accumulation of lead in roots was independent of the Pb concentration, whereas the accumulation of Pb in shoots was an almost linear function of the concentration of this element in the root medium. This treatment caused Pb concentration-dependent inhibition of apparent photosynthesis (APS), photorespiration (PR), <sup>14</sup>CO<sub>2</sub> uptake, stomatal opening and transpiration of shoots and also germination of seeds. The most sensitive to Pb contamination was CO<sub>2</sub> exchange, then transpiration and to a lesser degree germination of seeds. Lead caused a considerable alteration of photosynthetic and photorespiratory carbon metabolism, restricted the <sup>14</sup>C-labeling of: phosphoglycerate, ribose+ribulose, sucrose, glycolate and glycine+serine. Under conditions of C0<sub>2</sub> uptake limited by lead, an enhancement of the <sup>14</sup>C-labeling of malate+citrate, alanine and glucose was observed.

Lead accumulation and phytostabilization potential of dominant plant species growing in a lead–zinc mine tailing

Screening out plants that are hyper-tolerant to certain heavy metals plays a fundamental role in remediation of mine tailing. In this study, nine dominant plant species growing on lead–zinc mine tailing and their corresponding non-mining ecotypes were investigated for their potential phytostabilization of lead. Lead concentration in roots of these plants was higher than in shoots, and the highest concentrations of lead were found in Athyrium wardii: 15542 and 10720 mg kg−1 in the early growth stage (May) and vigorous growth stage (August) respectively, which were 426 and 455 times higher than those of the non-mining ecotypes. Because of poor lead translocation ability, lead accumulation in roots reached as high as 42 mg per plant. Available lead in the rhizosphere soils of A. wardii was 310 mg kg−1, which was 17 times higher than that of the non-rhizosphere soil. Lead concentrations of roots for the nine mining ecotypes were positively correlated with available lead in the rhizosphere soils, whereas a negative correlation was observed in the non-mining ecotypes. These results suggest that A. wardii was the most promising candidate among the tested species for lead accumulation in roots, and it could be used for phytostabilization in lead polluted soils.

Lead Induced Responses of Pfaffia glomerata, an Economically Important Brazilian Medicinal Plant, Under In Vitro Culture Conditions

Plantlets of Pfaffia glomerata (Spreng.) were exposed in vitro for 30 days to five lead levels (0-400 μM) to analyze the effects on growth and oxidative stress and responses of various antioxidants vis-à-vis lead accumulation. The plantlets showed significant lead accumulation in roots (1,532 μg g(-1) DW) with a low root to shoot lead translocation (ca. 3.6%). The growth of plantlets was negatively affected by various lead treatments, although the level of photosynthetic pigments did not alter significantly in response to any lead treatment. However, plantlets suffered from oxidative stress as suggested by the significant increase in malondialdehyde levels in root (8.48 μmol g(-1) FW) and shoot (3.20 μmol g(-1) FW) tissues with increasing lead treatments. In response to the imposed toxicity, increases in the activities of catalase in root (4.14 ∆E min(-1) mg(-1) protein) and shoot (3.46 ∆E min(-1) mg(-1) protein) and superoxide dismutase in root (345.32 units mg(-1) protein) and shoot (75.26 units mg(-1) protein), respectively, were observed, while the levels of non-protein thiols and ascorbic acid were not affected significantly in either roots or shoots.

Changes in non protein thiols, some antioxidant enzymes activity and ultrastructural alteration in radish plant (Raphanus sativus L.) grown under lead toxicity.

Forty days old radish plants (Raphanus sativus L.) were exposed to different regimes of lead stress as Pb(NO3)2 at the following concentrations 0, 25, 50, 100, 150, 250 and 500 ppm. The possible generation of oxidative stress, antioxidant metabolism and changes in the chloroplast and cell membrane ultrastructure were investigated. Greater loss of the photosynthetic pigments (Chl. a, Chl. b and total carotenoids) were observed especially under 500 ppm lead (Pb). The accumulation of lead in roots and leaves of plant were measured and the results showed that lead accumulation increased with increasing of the metal treatment concentration. An increasing trend was observed in levels of ascorbate and decreasing trend in glutathione. Also, the antioxidant enzymes, viz., guaiacol peroxidase (GPX) ascorbate peroxidase (APX), catalase (CAT) and glutathione S-transferase (GST) showed significant variation with the increase in lead stress compared to control (untreated) plants. The rapid inducibility of some of these enzymes is useful early and sensitive indicators of heavy metal toxicity. Native polyacrylamide gel electrophoresis revealed an increase in the isoenzymes profile of CAT in both leaves and roots. While POD isoenzymes bands prominently increased in leaves and slightly decreased in roots at the higher Pb concentration in the growth media. The ultrastructural studies at selected concentrations; 100 and 500 ppm of Pb showed distortion of the structure and cell membranes in roots. Therefore, the changes in the levels of some antioxidants may play an important role against oxidative injury.

Lead induced changes in antioxidant metabolism of horsegram ( Macrotyloma uniflorum (Lam.) Verdc.) and bengalgram ( Cicer arietinum L.)

One-month old horsegram ( Macrotyloma uniflorum (Lam.) Verdc. cv VZM1) and bengalgram ( Cicer arietinum L. cv Annogiri) were exposed to different regimes of lead stress as Pb(NO 3) 2 at 0, 200, 500 and 800 ppm concentrations. The extent of oxidative damage as the rate of lipid peroxidation, antioxidative response and the accumulation of lead in roots and shoots of both plants were evaluated after 12 days of lead stress. Lead (Pb) treated plants showed increased levels of lipid peroxidation as evidenced from the increased malondialdehyde content coupled with the increase in the activities of superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), glutathione reductase (GR), glutathione S-transferase (GST) compared to control (untreated) plants. Lead stress caused significant changes in the activity of antioxidative enzymes. The effect of lead was found to be concentration dependent. Higher concentration of lead (800 ppm) resulted 2- to 3-fold increase in SOD, catalase and peroxidase activities, 3- to 5-fold increase in GR activity and 3- to 4-fold increase in GST activity in roots and leaves of both horsegram and bengalgram plants. Lead stress caused a significant increase in the rate of peroxidation as showed in the levels of malondialdehyde content in roots and leaves of both plant species. Horsegram registered lower Pb accumulation than bengalgram, however localization of Pb was greater in roots than leaves in both plants. In general, lipid peroxide levels and antioxidative enzyme activities were higher in horsegram than bengalgram and also more in roots than leaves which best concordance with the lead contents of both the plants and organs. These results suggest that Pb toxicity causes oxidative stress in plants and the antioxidative enzymes SOD, CAT, POD, GR, GST could play a pivotal role against oxidative injury.

Accumulation and detoxification of lead ions in legumes

This study focuses on lead accumulation in roots, stems and leaves of three plant species of the Fabacea family: Vicia faba, Pisum sativum and Phaseolus vulgaris grown hydroponically in a medium supplemented with 1 mM concentration of lead. The largest amount of lead, up to 75 mg Pb/g dry weight, was accumulated in roots of P. vulgaris. The highest rate of Pb ions uptake from the medium took place during the first 10 h of incubation with lead and after 96 h of incubation lead content in the medium decreased by half. Thus, it was suggested that P. vulgaris could be used in rhizofiltration—the use of plant roots to absorb pollutants from water contaminated with lead. At the same time we studied the influence of lead on acid soluble thiol, glutathione, homoglutathione contents and the synthesis of phyto- and homophytochelatins in roots of V. faba, P. sativum and P. vulgaris grown hydroponically. Activation of the detoxicative-phytochelatin system was observed in the cytosol of root cells of the tested plants. This system was composed of phytochelatins (PCs) in roots of V. faba, homophytochelatins (hPCs) in P. vulgaris roots and both PCs and hPCs in P. sativum roots. The total content of PCs and hPCs in roots of P. sativum was very high and reached around 4800 (expressed in nmol SH×g −1FW) and induction of their synthesis occurred after only 2 h of treatment with 1 mM Pb.