ROS Metabolism of Citrus Fruits in Response to High-temperature-intense-light Stress

  Objective  The reactive oxygen species (ROS) metabolism of citrus fruits under high temperature and intense light was studied in search for means to mitigate sunburn damage on the fruits.

  Method  Sweet oranges, An-liu (Citrus sinensis Osbeck), grown in pots in an environmentally controlled chamber were exposed to artificial high-temperature-intense-light to create simulated burns on the fruits. Change on the ROS metabolism of the fruits as burn symptoms developed in normality and stages with appearance of dark yellow spots, slight browning, and seriously burnt coloration on the peel were monitored.

  Result  Under the imposed stress, the O₂^·- and MDA contents and LOX activity in pericarp significantly increased. The activities of SOD, POD, and PPO were significantly raised with the appearance of dark yellow spots on the peels. As the browning intensified, SOD significantly fell below the normal level, POD continued to increase, and PPO significantly decreased but remained to be higher than normal. Under the stress, AsA and GSH in the fruits decreased continuously.

  Conclusion  In the early stages, the high-temperature-intense-light stress began generating dark yellow spots on the orange pericarp. However, the fruit was able to sufficiently remove ROS diminishing or preventing damage on the cell membrane. Hence, it was the crucial time for implementation of measures to avoid sunburns on the fruits.