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(P) Oxidative Stress - Coggle Diagram

- - - - O2
        
        superoxide anions
        
        hydrogen peroxide
        
        hydroxyl/perhydroxyl radicals
      - redox reactions and incomplete oxygen reduction or water oxidation in mitochondrial and chloroplast electron transport
        
        respiration
        
        about 5% of the oxygen is reduced to highly reactive superoxides by leaking of electrons in the mitochondrial electron transport chain.
        
        Light reactions photosynthesis:
        
        H2O e- donor for chlorophyll
        
        Ferredoxine-NADP reductase (Mehler reaction)
        
        herbicides
        
        block the photosynthetic electron flow
        
        e.g. DCMU (Diuron), Paraquat
  - - - monolignol-polymerisation (crosslinking) & lignification (superoxide anions, H2O2)
      - as ‘signal molecules’, e.g. in response to pathogen attack (oxidative burst), but also in growth regulation
  - - - superoxide radicals (O2.-) are eliminated by superoxide dismutase (SOD),
        producing hydrogen peroxide (H2O2).
        
        H2O2
        
        converted to water and oxygen by catalase
        
        OR
        
        reduced to water by oxidation of ascorbate (vit. C)(ascorbate peroxidase, APX)
        
        ascorbate is regenerated in two ways:
        
        enzymatic reduction of monodehydro-ascorbate radicals in the plastids (with NADPH)
        
        spontaneous dismutation to dehydro-ascorbate, which then reacts with glutathion (dehydro-ascorbate reductase); glutathion is reduced with
        NADPH
        
        GSSG -> GSH
      - singlet oxygen (1O2) and (per)hydroxylradicals (OH., O2H.) are eliminated
        using
        
        glutathion, or non-enzymatically using vitamin E and carotenoids
    - - very reactive oxidant
        
        Negative effects:
        
        . reduced photosynthetic activity :sunny: (less Rubisco in mature leaves)
        
        . leaf damage :fallen_leaf:
        
        chlorotic lesions
        
        . reduced growth
        
        significantly reduced yields
        
        . accelerated senescence :fallen_leaf:
        
        Acclimation
        
        avoidance
        
        closing stomata
        
        tolerance
        
        . antioxidants
        
        . repair mechanisms
        
        . depending on environmental factors such as water,temperature, light, CO2 levels
  - - - H2O2
        
        SA
        
        biotic stress response
        
        secondary metabolites, e.g. fytoalexins
        
        cellular barrier molecules, e.g. callose, lignin
        
        pathogen response proteins, e.g. glucanase, chitinase, GST, PAL
      - increases ACC synthase & oxidase
        
        ethylene
        
        breakdown of cc walls
        
        death
      - interactions with methyl-jasmonate (MJ)
  - - - enhances tolerance to different abiotic stresses,
        improving cellular homeostasis and plant growth under stress conditions.