Study of phytochelatins and other related thiols as complexing biomolecules of As and Cd in wild type and genetically modified Brassica juncea plants

Abstract

The accumulation of As and Cd in Brassica juncea plants and the formation of complexes of these elements with bioligands such as glutathione and/or phytochelatins (PCs) is studied. The genetic manipulation of these plants to induce higher As and Cd accumulation has been achieved by overexpressing the genes encoding for gamma-glutamyl cysteine synthetase (gamma-ECS) and glutathione synthetase (GS). These two enzymes are responsible for glutathione (GSH) formation in plants, which is the first step in the production of PCs. The biomass produced in both the wild type and the genetically modified plants, has been evaluated. Additionally, the total Cd and As concentration accumulated in the plant tissues was measured by inductively coupled plasma mass spectrometry (ICP-MS) after extraction. Speciation studies on the extracts were conducted using size exclusion liquid chromatography (SEC) coupled online with ICP-MS to monitor As, Cd and S. For further purification of the As fractions, reversed phase high performance liquid chromatography (RP-HPLC) was used. Structural elucidation of the PCs and other thiols, as well as their complexes with As and Cd, was performed by electrospray-quadrupole-time-of-flight (ESI-Q-TOF). In both the Cd and As exposed plants it was possible to observe the presence of oxidized PC2 ([M + H]+, m/z 538), GS-PC2(-Glu) ([M + H]+, m/z 716) as well as reduced GSH ([M + H]+, m/z 308) and oxidized glutathione (GSSG) ([M + H]+, m/z 613). However, only the GS plants exhibited the presence of As(GS)3 complex ([M + H]+, m/z 994) that was further confirmed by MS/MS. This species is reported for the first time in B. juncea plant tissues.

An HPLC-ICP-MS technique for determination of cadmium–phytochelatins in genetically modified Arabidopsis thaliana

“…Some have also employed electrospray mass spectrometry (ESI-MS) for characterization [22][23][24]. However, the current separation schemes often yield inadequate resolution to separate individual cadmium-phytochelatin complexes.…”

Phytochelatins: Peptides Involved in Heavy Metal Detoxification

“…Navaza et al [10] performed structural elucidation of PCs and other thiols, as well as their complexes with As and Cd, by electrospray-quadrupole-time-of-flight (ESI-Q-TOF) in B. juncea plants overexpressed with genes encoding for gamma-glutamyl cystein synthetase (γ-ECS) and glutathione synthetase (GS). In both the Cd and As PCs interact with the metals through thiol (-SH) group of cysteine.…”

“…At present, at least 45 plant families with more than 400 plant species are known as metal accumulators [7,8]. Many species belonging to Brassicaceae have been found to sequester reasonable amount of various metals in their tissues [9,10,11]. Plants have constitutive and adaptive mechanisms for accumulating or tolerating high concentrations of their rhizospheric contaminants.…”

Agro-improving method of phytoextracting heavy metal contaminated soil

“…Most heavy metals (in phytoextraction) follow the roots-toleaves pathway, and not the other way. Usually, though heavy metals can be partially excreted by a plant, many of them integrate with some proteins or polypeptides [26][27][28] in a plant, so they are accumulated in some tissues and organs. Along with the growth of a plant, the contents of heavy metals accumulated in the plant gradually increase.…”