Speciation and Distribution of Arsenic in the Nonhyperaccumulator Macrophyte Ceratophyllum demersum      

Abstract

Although arsenic (As) is a common pollutant worldwide, many questions about As metabolism in nonhyperaccumulator plants remain. Concentration-and tissue-dependent speciation and distribution of As was analyzed in the aquatic plant Ceratophyllum demersum to understand As metabolism in nonhyperaccumulator plants. Speciation was analyzed chromatographically (highperformance liquid chromatography-[inductively coupled plasma-mass spectrometry]-[electrospray ionization-mass spectrometry]) in whole-plant extracts and by tissue-resolution confocal x-ray absorption near-edge spectroscopy in intact shock-frozen hydrated leaves, which were also used for analyzing cellular element distribution through x-ray fluorescence. Chromatography revealed up to 20 As-containing species binding more than 60% of accumulated As. Of these, eight were identified as thiol-bound (phytochelatins [PCs], glutathione, and cysteine) species, including three newly identified complexes: Cys-As(III)-PC 2 , Cys-As-(GS) 2 , and GS-As(III)-desgly-PC 2 . Confocal x-ray absorption near-edge spectroscopy showed arsenate, arsenite, As-(GS) 3 , and As-PCs with varying ratios in various tissues. The epidermis of mature leaves contained the highest proportion of thiol (mostly PC)-bound As, while in younger leaves, a lower proportion of As was thiol bound. At higher As concentrations, the percentage of unbound arsenite increased in the vein and mesophyll of young mature leaves. At the same time, x-ray fluorescence showed an increase of total As in the vein and mesophyll but not in the epidermis of young mature leaves, while this was reversed for zinc distribution. Thus, As toxicity was correlated with a change in As distribution pattern and As species rather than a general increase in many tissues.Arsenic (As) is ubiquitously present, considered a nonessential metalloid for plants and animals, and poses serious health hazards to humans. High levels of As in soil and drinking water have been reported around the world, with the worst situations in south and southeast Asia, where millions of people are at risk of As poisoning through drinking water and food (Chowdhury et al., 2000;Smedley and Kinniburgh, 2002;Ohno et al., 2007). Recently, As induced yield loss; thus, a threat to the sustainability of food production has been recognized as the other side of the As calamity (Brammer and Ravenscroft, 2009;Panaullah et al., 2009). Considering the enormity of As contamination, phytoremediation or the development of crops that can be grown in contaminated environments without suffering from and accumulating As in edible parts seem to be the most appropriate strategies to counter the detrimental impacts of As. These strategies demand an understanding of the mechanistic details of As uptake, toxicity, and detoxification . The in planta distribution and speciation of As are important aspects in this direction.Inorganic arsenate [HAsO 4 22 or As(V)] and arsenite [H 2 AsO 3 2 or As(III)] are the most common forms of As in aquatic and terrestrial environments. Plants take up...

Phytofiltration of arsenic and cadmium by using an aquatic plant, Micranthemum umbrosum: Phytotoxicity, uptake kinetics, and mechanism

“…Cys-As-(GS) 2 , and GS-As(III)-desgly-PC 2 in Ceratophyllum demersum macrophytes (Mishra et al, 2013). By contrast, Cd is likely to be taken up by a mechanism other than thiol formation.…”

Analysis of arsenic induced physiological and biochemical responses in a medicinal plant, Withania somnifera

“…In contrast, in plants exposed to AsV, only 50 and 100 μM caused a significant decline in GSH/GSSG ratio beyond 1 day (data not shown). Thiol metabolism plays important role in combating As stress (Mishra et al 2008) as thiols including GSH not only complex As through sulfur (Mishra et al 2013) and reduce the concentration of free As and allow its transport to vacuoles (Song et al 2010) but they also assist in the maintenance of redox status of the cell (Foyer and Noctor 2011), which is crucial for the functioning of various metabolic reactions (Srivastava et al 2011). Cysteine is the primary metabolite of sulfur assimilation pathway, which is then consumed for the synthesis of GSH and subsequently, GSH molecules are polymerized to produce phytochelatins (PCs) ).…”

Deficiency and toxicity of nanomolar copper in low irradiance—A physiological and metalloproteomic study in the aquatic plant Ceratophyllum demersum

“…Ceratophyllum demersum L. (the submerged, rootless macrophyte) was cultivated in an optimized nutrient solution for submerged macrophytes and water plants (SMNS, submerged macrophyte nutrient solution as used in our previous recent studies: Andresen et al, 2013aAndresen et al, ,b, 2016Mishra et al, 2013Mishra et al, , 2014Thomas et al, 2013). The strain has been continuously cultivated since 2005 in hydroponic cultures under 12 h day/12 h night light conditions with two Osram FLUORA ® fluorescent and two warm white fluorescent tubes and a temperature cycle from 18 • C at 6 a.m., over 20 • C at 9 a.m., to a maximum of 22 • C at 3 p.m., back over 20 • C at 9 p.m. to 18 • C again at 6 a.m. During the low light experiment a slightly different setup with light intensity to depict winter conditions (12 h sinusoidal light cycle with maximal irradiances at 38-40 E inside the aquaria and 12 h night) and temperature (19 • C at 6 a.m., 21.5 at 9 a.m., 24 at 3 p.m., 23 at 9 p.m., 19 at 6 a.m.) conditions were provided.…”

“…It has no roots, all nutrients are taken up over a large surface area of the entire shoot and it is sensitive to metal stress (Küpper et al, 1996(Küpper et al, , 1998Mishra et al, 2008Mishra et al, , 2009Mishra et al, , 2013Mishra et al, , 2014Andresen et al, 2013aAndresen et al, ,b, 2016Thomas et al, 2013). Our previous study (Thomas et al, 2013) analysed the effects of Cu deficiency and toxicity under high light conditions, like what C. demersum experiences in summer (Andresen et al, 2013b).…”