Heavy metals contribute to oxidative stress in algae

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Heavy metals contribute to oxidative stress in
algae Enue Sicairos Fresh Water and Marine
Algae
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Metals in the Environment

• Occur naturally part of organisms and food
  chain
• - Essential (Cu, Zn)
• - Toxic (Hg, Pb)
• Increase level due to anthropogenic activities
• -Industrial effluents
• -Agricultural fungicide runoff
• -Mining operations
• -Urban runoff
• Aquatic ecosystems are being affected
• -Chlamydomonas photosyntesis inhibited
• -Massachusetts bay

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Mechanism of toxicity

• 1.- Binding to sulphydryl groups in proteins
• 2.-Displacement of an essential element
• 3.-Induction of oxidative stress
• Increasing of reactive oxygen species (ROS)
• Reducing the cellular antioxidant capacity

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Reactive Oxygen Species (ROS)

• Small and highly reactive molecules (unpaired
  electrons)
• -oxygen ions, free radicals and peroxides
• They are normal byproducts of oxidative
  metabolism (respiration, photosynthesis)
• Environmental factor can increase ROS
• -Light
• -Heavy metal

O2 .- H2O2 .OH
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Cellular defense vs ROS

• Production of antioxidants
• Low molecular weight
• - ascorbate
• - carotenoids
• - flavonoids
• - phenolics
• - antioxidant glutathione
• High molecular weight
• - catalase
• - glutathione peroxidase (GPX)
• - ascorbate peroxidase (APX )
• - lipid peroxidase
• - superoxide dismutase (SOD)

Flavonoid
APX
Catalase
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(No Transcript)
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Scientific evidence

• 1.-Algae treated with Cd
• -Increased SOD activity in green algae
  Tetraselmis gracilis and Ditylum brightwellii
  (diatom).
• -Increased APX activity Selenastrum
  capricornutum(green unicellullar alga)
• -Decreased GSH content in the marine
  dinoflagellate L. polyedrum
• 2-Reductions in growth rates
• - Red algal species Asparagopsis armata (at 0.31
  ppm Cd2 and 0.092 ppm Cu2 )

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Conclusions

• Algae are the basis of the food web in all
  aquatic ecosystems.
• Stress treatments like high illumination,
  suddenly changes in temperatures increase of
  metal concentration affects an algal cells
  biochemical composition
• At high levels of metal pollutant damage to
  algal cells occurs because ROS exceed the
  antioxidant response.
• At low or chronic levels algae accumulate
  heavy metals and can pass them along the food
  chain.