Arsenic toxicity and speciation in plants, Arsenic toxicity and speciation in plants, Arsenic toxicity and speciation in plants, Arsenic toxicity and speciation in plants, implications for human nutrition implications for human nutrition

Lecture of Seema Mishra in the VK Bioinorganic Chemistry & Biophysics of Plants 2012

ArsenicArsenic

ArsenicArsenic

2, 8, 18, 5

Arsenic: occurrence Arsenic: occurrence

As is the twentieth most abundant element in the Earth’s crust with an average concentration of approximately 3 mg kg−1average concentration of approximately 3 mg kg 1.

More than 200 As-containing minerals exist; frequently As is associated with S in minerals such as arsenopyrites (FeAsS), realgar (As4S4), and orpiment (As2S3).

Arsenopyrites Realgar Orpiment

Arsenic: ApplicationsArsenic: Applications

The Poison of Kings and the King of Poisons Semiconductor industries Strengthening alloys of copper and lead Pesticides herbicides insecticides Pesticides, herbicides, insecticides Wood preservatives Feed additives Medical uses Military uses

Arsenic trioxide

Structures of the most common As compounds

Trimethyl Arsiney

Sources of Arsenic ContaminationSources of Arsenic Contamination

Through anthropogenic activities such as mining, smelting, phosphate fertilizer, and the use of As-containing pesticides, herbicides, wood preservatives, and feed additives.

Through natural processes such as weathering of rocks volcanic Through natural processes, such as weathering of rocks, volcanic emissions and discharge from hot springs

Arsenic ContaminationArsenic Contamination

Arsenic ContaminationArsenic Contamination

Basic Facts of the ProblemBasic Facts of the Problem

The current limit of As in drinking water (WHO) is 10 μg/L.

WHO Provisional Maximum Tolerable Daily Intake (MTDI) limit of As is 2 μg/Kg body weight.μg g y g

Level of As in drinking in West Bengal above 50 μg/L are commonly found Severely affected areas may contain as high as 2000 μg/Lfound. Severely affected areas may contain as high as 2000 μg/L.

If rice grain with an As level of 0.1 μg/g (a typically normal As level) is consumed at a rate of 420 g/day (representative of rice-based diet), then ingestion of 0.7 μg/Kg (35% of MTDI) body weight would occur.

Far exceeding levels e.g. up to 3 μg/g are found. In addition, cooking rice in contaminated water also adds to As consumption.

Arsenic ExposureArsenic Exposure

Toxicity to human Toxicity to human

Acute effects Gastrointestinal effects (Nausea Diarrhea Abdominal pain) Gastrointestinal effects (Nausea, Diarrhea, Abdominal pain) Effects on central nervous system and cardiovascular system Liver and kidney dysfunction Anemia, leukopenia Ingestion of 600 µg/kg body weight/day or inhalation of 25-50 ppm

arsine for a half- hour is lethalarsine for a half hour is lethal Chronic effects Gastrointestinal effects, Skin lesions, hyperpigmentation, Anemia, peripheral neuropathy, gangrene of the extremities, vascular

lesions, and liver or kidney damage, y g Increased risk of Cancer : skin, bladder, liver, and lung cancer

Toxicity to human Toxicity to human

(www.soesju.org)Richard Wilson, Harvard University, and Dhaka Community Hospital

Arsenicosis patients from arsenic-affected areas

Why Rice ?Why Rice ?

Pick your poison ?

Why Rice ?Why Rice ?

Meharg (2004). TRENDS in plant science, 9, 415-417.

Arsenic Toxicity to Plants Arsenic Toxicity to Plants

Symptoms

Reduced germination, Inhibited root growthInhibited shoot growthInhibited shoot growth Reduced chlorophylls Low grain yieldTo death

Castillo-Michel et al. (2007). Plant Physiol. Biochem. 45, 457-463

Arsenic Toxicity to Plants Arsenic Toxicity to Plants

Mechanism

Through uptake competition for essential nutrients

Through substitution of phosphate by iAs(V) in enzyme catalyzed oug subs u o o p osp a e by s( ) e y e ca a y edreactions

By binding of iAs(III) to sulfhydryl group containing enzymesy g ( ) y y g p g y

ROS generation

Reduction of iAs(V) to iAs(III) using glutathione as reductant

Oxidation of iAs(III) to iAs (V) under physiological conditions

Arsenic Toxicity to Plants: Arsenic Toxicity to Plants: GenotoxicityGenotoxicityInduction of micronuclei by heavy metal(loid)s

Tradescantia Stem Root tip of Allium cepa Root tip of Vicia faba

As3+> Pb2+> Cd2+> Zn2+> Cu2+ Trad MCN> Vicia root MCN> Allium root MCNSteinkellner et al. (1998). Environmental and Molecular Mutagenesis 31, 183-191

Arsenic Toxicity to Plants: Arsenic Toxicity to Plants: GenotoxicityGenotoxicity

leaves

Root

Comet images of plant nuclei of Vicia faba under arsenate treatments

Lin et al. (2008). Environ Toxicol. Chem. 27, 413–419

Arsenic Toxicity to Plants: Proteomics Arsenic Toxicity to Plants: Proteomics

Control 300 µM As(V) 250 µM As(III)

A ; down regulatedB-D; up regulated

CeratophyllumCeratophyllum demersumdemersum L.L.

CeratophyllumCeratophyllum demersumdemersumCeratophyllumCeratophyllum demersumdemersumis rootless aquatic weedis rootless aquatic weed

showsshowsRapid growthRapid growth

and Worldwide distributionand Worldwide distributiond b E il h t dd b E il h t dand can be Easily harvestedand can be Easily harvested

Arsenic Metabolism in nonArsenic Metabolism in non--hyperaccumulatorhyperaccumulator plantsplants

APSSO 2- SO42-

ATP sulfurylase

SulfiteAPR

SulfideSiR

APSSO4 SO4 Sulfite Sulfide

OAS

SAT

CysCS

ECECS

GSHGS

GluGly

AsIII AsIII PCs

AsIIIPCS

?

GSH

GSSG

As-Thiol AsIII, As-Thiol

ABCC

AsV AsV AsIII

?

Phytochelatins (PCs) are glutathione derived metal binding peptides with

AsIII

Phytochelatins (PCs) are glutathione derived metal binding peptides with general structure (γ -Glu-Cys)n Xaa, where n = 2–11 and Xaa is generally Gly.

As As HyperaccumulationHyperaccumulation in in pterispteris vittatavittata (Chinese Brake fern)(Chinese Brake fern)

/ ( )Accumulates up to 22,000 mg As /kg (DW) Up to 2.3-4.1% of biomass

As speciation analysisAs speciation analysis

ICP-MS ESI-MSHPLC

Phytochelatin synthase from C. demersum

TransgenicWT TransgenicWT TransgenicWT TransgenicWTTransgenicWT TransgenicWT

0 µM 100 µM 300 µM 0 µM 100 µM 200 µM

w w

Cd

(µg

g-1

dw

As (µ

g g-

1dw

Cd Concentration (µM) As(V) Concentration (µM)

Arsenic: a building block of life

New Bacteria Makes DNA With Arsenic: NASA Life Discovery

The arsenic rich Mono Lake California A scanning electron micrograph ofThe arsenic-rich Mono Lake, California A scanning electron micrograph of the arsenic-based bacteria

A Bacterium That Can Grow by Using Arsenic Instead of Phosphorus

Wolfe-Simon et al (2011), Science. 332, 1163-1166

A Bacterium That Can Grow by Using Arsenic Instead of Phosphorus

Can arsenic bind to bacterial DNA ?

DNA structure with arsenic replacing phosphorus in the backboneJ Wang, J Gu and J Leszczynski, Chem. Commun., 2012, DOI: 10.1039/c2cc16600c