Selected Morphological Characteristics, Lead Uptake and Phytochelatin Synthesis by Coffeeweed (Sesbania exaltata Raf.) Grown in Elevated Levels of Lead-Contaminated Soil

Maria F. T. Begonia,Gregorio Begonia,Gloria Miller

doi:10.3390/ijerph8062401

Abstract

Remediation of lead-contaminated soil is significant due to the inherent toxicity of lead (Pb), and the quantity of Pb discharged into the soil. One of the most cost-effective and environmentally sound technologies for the cleanup of metal-contaminated soils is through the use of plants. While much is known about the ecological evolution of metal tolerance in plants, the physiological, biochemical, and genetic mechanisms of tolerance is not well understood in the majority of resistant ecotypes such as the legume, Sesbania exaltata Raf. This study was therefore conducted to determine the morphological and physiological characteristics of Sesbania that had been grown in Pb-contaminated soil, and to assess phytochelatin synthesis as a way of elucidating its relative Pb tolerance. Sesbania plants were grown in the greenhouse and exposed to various levels of Pb: 0, 1000, and 2000 mg Pb/kg soil. Plants were harvested after 6, 8, and 10 weeks of growth and morphological characteristics (e.g., root and shoot biomass, root length, number of root nodules, shoot height, number of leaves, number of flowers, number and length of pods) were recorded. Generally, there were no statistical differences in morphological characteristics among the treatments. Further, no discernible phytotoxic symptoms, such as chlorosis, wilting, or necrotic lesions, in neither roots nor shoots were observed. We concluded that while Sesbania did not fit the model of a hyperaccumulator, the plant was, nonetheless, tolerant to elevated Pb levels. Our assessment for phytochelatin synthesis as a tolerance mechanism was inconclusive and further investigations of tolerance mechanisms are warranted.

Highlights

Soil contamination by heavy metals such as cadmium (Cd), copper (Cu), nickel (Ni), Zinc (Zn), andPb has become a critical environmental concern due to potential chronic and acute ecological effects [1]
In order to minimize discrepancies in the results that could arise from heterogeneous soil samples, a laboratory amended Pb-spiked soil sample was used throughout this experiment so that we could create a test sample with consistent lead concentration and speciation, soil composition, contamination process, and contamination period
The soil sample used in this experiment is a member of the fine Kaolinitic, thermic typic

Summary

Introduction

Soil contamination by heavy metals such as cadmium (Cd), copper (Cu), nickel (Ni), Zinc (Zn), andPb has become a critical environmental concern due to potential chronic and acute ecological effects [1]. Phytoremediation is emerging as cost-effective and environmentally sound cleanup of metalcontaminated soils [4] in part because the costs of growing plants are minimal compared to those of soil removal and replacement [5]. A subset of phytoremediation known as phytoextraction is the use of plants to remove inorganic contaminants, primarily metals, from polluted soil. In this approach, plants capable of accumulating high levels of metals are grown in contaminated soil [6]. The success of phytoextraction as an environmental cleanup technology, depends on several factors including the extent of soil contamination, metal availability for uptake into roots (bioavailability), and the plant's ability to intercept, absorb, and accumulate metals in shoots [10]

Objectives

Methods

Results

Conclusion