Characterization of the High Molecular Weight Cd-Binding Complex in Water Hyacinth (Eichhornia crassipes) When Exposed to Cd

Abstract

Water hyacinth ( Eichhornia crassipes) is a rapid-growing freshwater vascular plant that has been used to remove heavy metals in contaminated water. But the transportation and distribution of the absorbed heavy metal in the plant are not clear. In this study, water hyacinth was exposed to cadmium (Cd, 10 microM, pulse) and then transferred to a Cd-free solution (chase). The Cd content in the tissues was measured, and the Cd-binding complexes were isolated and identified. We found that (1) in two days, up to 80% of the Cd in the solution was absorbed by the plant, and the Cd could not be released back to the growth solution in the chase period; (2) approximately 1 mg of Cd was accumulated in the water hyacinth/g of dry weight in this condition; (3) invading Cd was bound rapidly as the low-molecular-weight (LMW) complex serving as the transient form for further sequestration; (4) the LMW complex in water hyacinth contained no phytochelatins and was different from the LMW complex in fission yeast; (5) the Cd absorbed in the plant was essentially stored in the high-molecular-weight (HMW) form after 1 week; (6) a small fraction of the absorbed Cd was found in the upper part of the plant (stem and leaves) in the form of complexes; (7) the HMW complex was composed of phytochelatins PC 3 and PC 4 primarily, with only a small amount of PC 2; (8) a rare PC-related peptide was found in the HMW complex that might be derived from PC 3. These observations contribute to the further understanding of water hyacinth in serving as an efficient and reliable accumulator for heavy metals.

Identification of the binding forms of cadmium during accumulation by water hyacinth

“…According to the published data concerning these species determination, the results obtained by different researchers are often not in agreement with each other. [9,10] In some cases, the preference is given to the protein nature compounds -metallothioneins, [9] whereas phytochelatins which are the products of the enzymatic synthesis are most often considered as chelators in plants. [10,11] To identify the main cadmium binding forms in water hyacinth, we proposed the methodology, the essence of which is illustrated by the scheme (Figure 1).…”

“…Sample preparation procedure for the elements determination by ICP-OES in plant's tissues included a digestion procedure in the presence of the reactant's mixture containing 5 mL of HnO 3 , 2 mL of HCl, and 0.4 mL of HF per 0.10 g of plant tissue using microwave-assisted system according to the program: (1) 10-min ramping to 90 °C, 10-min holding at 90 °C; (2) 10-min ramping of non-protein nature, [10] and at a longer exposuremetal depositing in plant's root tissues as a complex with peptides, which are the products of enzymatic synthesis -phytochelatins with the polymerization degree of 3-4. Cadmium compounds of protein nature relating to phytochelatins were also found in the leaves while some of them have not been identified.…”

“…At the same time, there is an evidence of the binding of cadmium with peptides, which are the products of enzymatic synthesis -phytochelatins. [10,11] Amino acid composition was determined in cadmium-containing fractions and in the areas of the chromatogram where no cadmium was detected to confirm the absence of peptide compounds in them. The results of amino acids quantification are presented in Table 4.…”

In vitro micropropagation of water hyacinth (Eichhornia crassipes)

“…Moreover, noteworthy results were also observed in using plant agar which had almost doubled the root number and length though the fresh weight was just half. In addition, removal of nitrate, soluble phosphorous (Reddy et al 1982;Reddy et al 1983), and heavy metals (Wu et al 2008) is highly related to the root system. For example, water hyacinth can remove 81% of arsenic through its fibrous roots (Quayum 2007).…”

“…Water hyacinth is native to Brazil of South America, and is regarded as an invasive weed plants because of its vigorous ability of propagation by stolon and seeds. It is also known as the most representative and a fast-growing aquatic macrophyte for water purification, and has been used to remove heavy metals in contaminated water (Mishima et al 2006;Wu et al 2008). Nutrient removal from wastewater has become an important issue due to the problems of eutrophication in many areas of the world.…”