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ADVANCES IN BIOTEC HNOLOGY
BCH-751
Understanding Oxidative Stress andAntioxidant
Functions to Enhance Photosynthesis
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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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