PROTECTION AGAINST SUNSCALD IN APPLE FRUIT BY THE ASCORBATEGLUTATHIONE CYCLE

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PROTECTION AGAINST SUNSCALD IN APPLE FRUIT BY THE
ASCORBATE-GLUTATHIONE CYCLE

• PK Andrews, JR Johnson D Fahy
• Washington State Univ
• Pullman, USA

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ACKNOWLEDGEMENTS

• Funding by
• Washington State Tree Fruit Research Commission
• Abbott Laboratories
• Grower cooperators
• Auvil Fruit Company, Inc.
• Allan Brothers, Inc.

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MATERIALS METHODS

• Malus domestica Borkh. Fuji
• Commercial orchards in central Washington state
  (48oN)
• Plots
• Control
• Shade cloth (21)
• Evaporative cooled with sprinklers
• Sample fruit - sunlight exposed

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MEASUREMENTS

• Surface skin temperature (midday)
• Incidence of sunscald
• Biochemical
• Ascorbic acid (AsA) dehydroascrobate (DHA)
• Glutathione, reduced (GSH) oxidized (GSSH)
• Chlorophyll a b
• Total carotenoids anthocyanins
• Anatomical - epidermal hypodermal

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FRUIT SKIN TEMPERATURE

• Control fruit
• Up to 11.1-13.9oC hotter than air temperature
• Shade cloth
• Averaged 2.2oC cooler than control fruit
• Up to 7.2oC cooler
• Evaporative cooling
• Averaged 2.2oC cooler than control fruit
• Up to 11.1oC cooler

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CONCLUSIONS

• Seasonal changes in ascorbate/glutathione cycle
  antioxidants coincided with observed differences
  in sunscald susceptibility
• Antioxidant concentrations varied when
  light/temperature regimes were modified
• Incidence of sunscald was reduced when ascorbic
  acid was applied
• Sunscald-damaged fruits had reduced levels of
  antioxidants

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SUNSCALD HYPOTHESIS

• Generation of active oxygen species and
  photooxidative damage results when
• Low demand for carbon assimilation, i.e. less
  respiratory CO2 during pre-climacteric period for
  re-fixation by PEP carboxylase
• Excess supply of reducing energy, i.e. excess
  excitation of persistent chlorophyll under high
  light/temperature regimes