SM Arsenic toxicity and speciation in plants implications ...€¦ · Arsenic toxicity and...
Transcript of SM Arsenic toxicity and speciation in plants implications ...€¦ · Arsenic toxicity and...
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