Transcript Heavy metals contribute to oxidative stress in algae Enue Sicairos Fresh Water and Marine Algae.

Heavy metals contribute to oxidative stress in algae
Enue Sicairos
Fresh Water and Marine Algae
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
Mechanism of toxicity
1.- Binding to sulphydryl groups in proteins
2.-Displacement of an essential element
3.-Induction of oxidative stress
a)
b)
Increasing of reactive oxygen species (ROS)
Reducing the cellular antioxidant capacity
Reactive Oxygen Species (ROS)
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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
Cellular defense vs ROS
Production of antioxidants
Low molecular weight
- ascorbate
-
carotenoids
flavonoids
phenolics
antioxidant glutathione
Flavonoid
High molecular weight
- catalase
-
glutathione peroxidase (GPX)
ascorbate peroxidase (APX )
lipid peroxidase
superoxide dismutase (SOD)
APX
Catalase
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+ )
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 cell’s 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.