Uptake, translocation and transformation of arsenate and arsenite in sunflower (Helianthus annuus): formation of arsenic–phytochelatin complexes during exposure to high arsenic concentrations

Abstract

Summary• The aim of the study was to determine the time-dependent formation of arsenicphytochelatin (As-PC) complexes in the roots, stems and leaves of an arsenicnontolerant plant ( Helianthus annuus ) during exposure to 66 µmol l − 1 arsenite (As (III) ) or arsenate (As (V) ).• We used our previously developed method of simultaneous element-specific (inductively coupled plasma mass spectrometry, ICP-MS) and molecular-specific (electrospray-ionization mass spectrometry, ES-MS) detection systems interfaced with a suitable chromatographic column and eluent conditions, which enabled us to identify and quantify As-PC complexes directly.• Roots of As-exposed H. annuus contained up to 14 different arsenic species, including the complex of arsenite with two ( γ -Glu-Cys) 2 -Gly molecules [As (III) -(PC 2 ) 2 ], the newly identified monomethylarsonic phytochelatin-2 or ( γ -Glu-Cys) 2 -Gly CH 3 As (MA (III) -PC 2 ) and at least eight not yet identified species. The complex of arsenite with ( γ -Glu-Cys) 3 -Gly (As (III) -PC 3 ) and the complex of arsenite with glutathione (GSH) and ( γ -Glu-Cys) 2 -Gly (GS-As (III) -PC 2 ) were present in all samples (roots, stems and leaves) taken from plants exposed to As. The GS-As (III) -PC 2 complex was the dominant complex after 1 h of exposure. As (III) -PC 3 became the predominant As-PC complex after 3 h, binding up to 40% of the As present in the exposed plants.• No As-PC complexes were found in sap (mainly xylem sap from the root system), in contrast to roots, stems and leaves, which is unequivocal evidence that As-PC complexes are not involved in the translocation of As from root to leaves of H. annuus .

Arsenic accumulation by the aquatic fern Azolla: Comparison of arsenate uptake, speciation and efflux by A. caroliniana and A. filiculoides

“…Similar to other studies on higher plants (e.g. Koch et al, 2000;Quaghebeur and Rengel, 2003;Raab et al, 2005;Xu et al, 2007), we found arsenite and arsenate to be the dominant forms of As in the two strains of Azolla, with methylated As compounds accounting for <5% of the total As. However, the two Azolla strains showed a significant difference in the proportions of arsenite versus arsenate, with A. filiculoides having a higher percentage of arsenite (55-70%) than A. caroliniana (25-40%) (Fig.…”

Arsenate-Resistant Genes in Egyptian Rice Cultivars as Soil Pollution Sensors

“…Till now there are no literature deals with the function of the CwfJ family protein except some reports which considered it as one of the defence proteins. It was suggested that these genes work in combination to resist the toxic effect of the arsenate and this agree with what postulated by Raab [44]. The mechanism of how they tolerate high (As) burdens in their tissues is not well understood, although tolerance is not due to enhanced phytochelatin production or metabolism of inorganic As to organic species.…”

“…However, other models of plant tolerance to As V have been recently found and reported in tomato and rice [64]. The mechanism of how they tolerate high As burdens in their tissues is not well understood, although tolerance is not due to enhanced phytochelatin production or metabolism of inorganic As to organic species [44]. Some plant species exhibit phenotypic variation in response to arsenic species giving idea about arsenic toxicity and the way with which plants have evolved arsenic resistances.…”

Identification of Genes Related to Arsenic Detoxification in Rice Roots Using Microarray Analysis

“…As concentration in rice and some vegetables are exceed the safety limits [3]. Previous studies have reported the molecular mechanism in plants during As stress [4], [5]. However, these studies carried out in the plants exposed to high As concentrations, little is known on rice roots subjected to low concentration of AsV.…”

“…After entering into roots, AsV is reduced to AsIII which is subsequently detoxified by phytochelatins (PCs). Studies showed that phytochelatins (PCs) play an important role in the detoxification of As [4], or heavy metals [7]. AsV-PCs complexes sequestered into vacuoles by glutathione-conjugating pumps, and then form a more complex aggregation in the vacuole [8].…”