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ANTIOXIDANT SYSTEMS IN FRUIT

ANTIOXIDANT SYSTEMS IN FRUIT. Preston K. Andrews Department of Horticulture and Landscape Architecture Washington State University. ACKNOWLEDGMENTS. Partial funding by: Washington State Tree Fruit Research Commission Abbott Laboratories Cooperators: Auvil Fruit Co. & Allan Bros., Inc.

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ANTIOXIDANT SYSTEMS IN FRUIT

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  1. ANTIOXIDANT SYSTEMS IN FRUIT Preston K. Andrews Department of Horticulture and Landscape Architecture Washington State University

  2. ACKNOWLEDGMENTS • Partial funding by: Washington State Tree Fruit Research Commission Abbott Laboratories • Cooperators: Auvil Fruit Co. & Allan Bros., Inc. • Research team: Dr. Jim Johnson Nichole Gish Deirdre Fahy Jennifer Halliday Peggy Collier Sean Spratt

  3. LIGHT ENERGY PATHWAYS LIGHT ENERGY Thermal energy dissipation Fluorescence Mehler-peroxidase reaction sequence Photorespiration Photosynthetic CO2 assimilation

  4. FRUIT PHOTOSYNTHESIS • Non-autotrophic • Large diffusive resistance • Low stomatal frequencey (10-100X < leaf) • Epicuticular wax • C3 chloroplast structure • Low Chl a:b ratio (1-3) • High internal [CO2] (1-4%) • Fruit C primarily from leaf RUBISCO

  5. FRUIT PHOTOSYNTHESIS • Both PSI & PSII operative • Dark fixation of HCO3 by PEP carboxylase • Malate accumulation in vacuole • Photorespiration (?)

  6. PHOTOOXIDATIVE STRESS • Generation of toxic derivatives of oxygen by light-dependent processes • Photosensitized pigments (3Chl*) transfer energy to oxygen to form 1O2 • Electron carriers with negative electrochemical potentials allow e– transport to oxygen to form O2–.

  7. FREE RADICALS • Any unbound chemical species with an odd number of electrons (single electron occupying an atomic or molecular orbital) Superoxide anion O2– . Hydroxyl HO. Singlet oxygen 1O2 Alkoxyl alkO. & alkylperoxyl alkOO.

  8. RADICAL CHAIN REACTIONS • Initiation • Photosensitizer (3Chl*) + O2 O2–. • Unsaturated fatty acid +O2 (via 1O2)  alkOn. • Propagation: atom or electron transfer • Termination • Radical scavenging by glutathione, ascorbate or -tocopherol • Dismutation by superoxide dismutase (O2–. H2O2)

  9. XANTHOPHYLL CYCLE • Carotenoid pigments bound to light-harvesting antenna complexes • Conversion of excess light energy into heat • Induced by acidification within thylakoid • High light: Violaxanthin  antheraxanthin  zeaxanthin Violaxanthin deepoxidase • Ascorbate reductant

  10. CAROTENOIDS zRabinowitch et al, Planta 122:91, 1975 yGross et al, J Plant Physiol 89:312, 1978 (cv Golden Delicious) xIncludes minor amounts of - and -carotenes

  11. Ascorbate-glutathione cycle Mehler-peroxidae rxn GSSH SOD ASC O2. H2O2 NADPH NAD(P) PS APX PSI MDAR DHAR GR NAD(P)H O2 NADP H2O MDA GSH DHA MEHLER-PEROXIDASE CYCLE

  12. BORON APPLICATION Ascorbic acid (mg/100g FM) a b Mondy & Munshi, J Agric Food Chem 41:554, 1993

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