BCH 751 Presentation

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ADVANCES IN BIOTEC HNOLOGY

BCH-751

Understanding Oxidative Stress andAntioxidant

Functions to Enhance Photosynthesis

May 5, 2012

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RAJA TAHIR MAHMOOD

07-ARID-1642

PH.D BCH (1ST )

Understanding Oxidative Stress and AntioxidantFunctions to Enhance Photosynthesis


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Contents

Oxidative stress

Reactive Oxygen Species

Lipid/ protein oxidation

Antioxidant

Photosynthesis

Photosynthetic regulation

by ROS

Antioxidant network in

chloroplast

Genetic engineering

approach

Antioxidant signaling

Summary

References

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Oxidative stress

Oxygen.. to produce energy Generate during photosynthesis

Also produce reactive oxygen species OH-, O2-,H2O2

Reduced by antioxidant

Imbalance between production and reduction..Oxidative stress

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Impact

Immunogenic

ROS damage macromolecules

DNA Protein

Lipids

Diseases. Cancer, aging, arthritis etc.

Reduce rate of photosynthesis

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ROS production

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Reactive Oxygen Species

ROS are;

Highly reactive

Short life span

Cascade of reaction

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Protein/ Lipid oxidation

O

N

HO

N

H

RH

.HO.

RO

N

HO

N

H

R

R

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Antioxidants

Detoxify reactive oxygen intermediates (ROI)

Compounds (Melatonin, ascorbate, glutathione)

Enzymes (peroxiredoxin, SOD, Catalase)

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Conti..

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Photosynthesis

Converts CO2 into organic compounds

Use sunlight energy

Two phases..

Light dependent phase Light independent phase

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Light-dependent phase

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Light-independent phase

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Photosynthesis and oxidative stress

Photosynthesis source of ROS

regulatory systems are required;

to minimize ROS production

efficient antioxidant network.....ROS at low level

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Conti.

ROS unavoidable by-product.. oxygenic

photosynthesis

Thought as damaging but

Current research confirm role

Signaling

Plant growth

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Conti.

Increase ROS production. Increase oxidation

Decrease PS-II

Defense gene expression

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ROS production during Photosynthesis

Water oxidation at PS-II.. Produce e-

Proton gradient for ATP

FNR.. NADPH

Singlet oxygen oxidize D1 protein

Normally PS-II repair itself

Damage exceed .repairing.. photoinhibition

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Conti.

Cyclic electron flow;

More ATP production

Avoid singlet oxygen production at PS-II

Produce superoxide and H2O2

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OxidantProduction

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Antioxidantnetworkofchloroplasts

Photosynthesis source of oxidants

O-2..damage PS-II

H2O2 Inhibit photosynthesis inhibit CO2 fixation

So balance is necessaryROS production and scavenges

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Conti.

Ascorbate (AsA) and Glutathione (GSH)

Water soluble antioxidant

Present in chloroplast

AsA-GSH cycle

metabolize H2O2

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AsA-GSH cycle

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Conti..

Photosynthetic limitations

AsA absence APX oxidative inactivation

Half inactivation 30s

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PRX-GPX Cycle

Peroxiredoxin- Glutathione peroxidase cycle

Thioredoxin (TRX) dependent

Recycled to conti. cycle

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PRX-GPX Cycle

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Conti

GPX can use GSH and TRX substrate

TRX more efficient substrate

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APX-cycle ORGPX-cycle

APX more affinity for H2O2

GPX can detoxify lipid peroxide, NO

Both cycle are important

Environmental conditions

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Interaction between two cycles

Arabidopsis thaliana, suppressed chloroplast located

PRX. Enhanced MDA reductases and APXs

production

Compensate each other functions

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Conti

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Other Antioxidants

hydrophobic antioxidant, a -tocopherol (Toc)

In reduced form by AsA

Reduced singlet oxygen

Lipid peroxyl radicals

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Alpha tocopherol action

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Interaction with AsA-GSH cycle

A. thaliana,vitamin E deficient1 (vte1)...... Highconc. of AsA and GSH

VTE1- over expressing plants. LOWAsA andGSH level

Suggesting interaction

Compensate each other

Multiple controlling site

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Future understanding

Biosynthesis of Toc, GSH and AsA are wellunderstood

So, further understanding require

Synthesis and

Accumulation in coordinated way

Intracellular partitioning

Photosynthesis regulation

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Genetic Engineering approaches

Many strategies are used to protect from abioticstress;

Enhance stress tolerance

Photosynthetic inhibition

Over expression of GR, DHAR, SOD in chloroplast

Effective way of protecting plants

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ROS generation for signaling

Enhancement of antioxidant capacity ..protection to photosynthesis

Suggesting;

Not an excess capacity for ROS destruction coordination . between production and destruction

ROS redox signaling;

ROS production Lifetime become apparent

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Genetic engineering approaches

Increase antioxidant network . increase stressresistant

Transgenic tobacco and Arabidopsis over expressing thylakoid membrane bound APX

enhanced tolerance to high light.. photooxidative stress

Transgenic tobacco CatE Escherichia coli catalase.. Stroma

enhanced tolerance

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Conti..

KatE compensate APX inactivation

APX inactivation . Possible redox signaling

High ROS production

Oxidative stress

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Conti.

Cyanobacterial flavodoxin expression in higher

plants.. enhanced tolerance to abiotic stresses

prevent electron misrouting

Reducing ROS formation

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Metabolite antioxidant

Galactinol , raffinose and glycinebetaines Antioxidant

osmoproctants

Differ from other.. not recycled

Enhance glycinebetainebiosynthesis increase

oxidative stress tolerance It produce H2O2 Activate ROS -scavenging enzymes

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Antioxidant signaling

deficient in cytosolicAPX tobacco plants lessmarked phenotype

ROS and antioxidants participate;

Programme cell death

Enhance defense for survival

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Conti.

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Conti..

Singlet oxygen.. Programme cell death (PCD)

H2O2 .. PCD using salicylic acid

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Conti.

Chloroplastic ROS, AsA and GSH interact withphotosynthetic machinery

Participate in signaling pathway Help to adopt environmental stress

The high light stress signaling pathways also interact

with hormone signaling pathways

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Retrograde signaling

These signaling pathways involve retrogradesignaling

Regulate genes .. Env. Stresses

Oxidants and antioxidants may control interactionbetween pathways much need to clear yet

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Summary

ROS are unavoidable species of oxygenic

photosynthesis

Imbalance between production and utilization maycause oxidative stress

Antioxidants clear these from cell to protect from

damage

ROS and antioxidant production act as signaling

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Enhancing antioxidant enzymes activities by genetic

manipulation increases stress tolerance

through efficient removal of ROS Photosynthetic processes are desensitize d to environmental

changes

Antioxidant systems have evolved not to completely

remove ROS but to allow these signals to persist

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Summary

The persistence of ROS in stressful environmentalconditions serves to limit the capacity ofphotosynthesis

Manipulations of plant antioxidant defenses havebeen largely limited to a small number of enzymes

More can be exploit, having protective functions, tomake photosynthetic process more better

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References

Dietz K J (2011) Peroxiredoxins in plants and cyanobacteria. Antioxid Redox Signal (in press).

Ishikawa T, Shigeoka S (2008) Recent advances inascorbate biosynthesis and the physiological significance of

ascorbate peroxidase in photosynthesizin g organisms.Biosci Biotechnol Bioche m 72: 11431154

Krieger-Liszkay A , F ufezan C, Tre bst A (2008 ) Singletoxygen production in photosy stem II and related

protection mechanism. Photosynth Res 98: 551564 Munekage YN, Genty B, Peltier G (2008) Effect o f PGR5

impairment on photosynthesis and growth in Arabidopsisthaliana. Plant Cell Physiol., 49: 1688 1698

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References

Mittler R, Blumwald E (2010) Genetic engineering formodern agriculture :challenges and perspectives. Annu RevP lant Biol 61: 443462

Vass I , Cser K (2009) Janus-faced ch arge recombinations

in photosystem II photoinhibition . Trends Plant Sci 14:20020 5

Vass I , Aro E M (2008) Photoinhibition of photosyntheticelectron trans-port. In G Rengered, Primary Processes of

Photosynthesis: Basic Principles and Apparatus . Roy alSociety o f Chemistry, Cambridge, UK, pp 393411

Zurbriggen MD, Tognetti V B, Fillat MF, Hajirezaei MR, Valle EM,Carrillo N (2008) Combating stress with flavodoxin : a promising routef or crop improvement . Trends Biotechnol 26: 531537

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