Title: Response of the ascorbate-glutathione cycle to storage temperature in carambola fruit Authors
Submitted to: Southern Region of the American Society for Horticultural Science
Publication Type: Abstract Only
Publication Acceptance Date: February 12, 2010
Publication Date: N/A
Technical Abstract: The generation of reactive oxygen species (ROS) is considered to be a primary event under a variety of stress conditions. It has been generally accepted that reactive oxygen produced under stress is a detrimental factor, which causes lipid peroxidation, enzyme inactivation, and oxidative damage to DNA, before visible symptoms. To control the level of ROS and to protect cells under stress conditions, plant tissues contain several enzymes that scavenge ROS. The ascorbate-glutathione cycle, also called Halliwell-Asada pathway plays an important role in scavenging ROS and in continual production of antioxidants. Carambola fruit harvested at the half yellow to yellow stage were stored at 2, 5, 10, 15 and 20 °C for 21 days then transferred to 20 °C for 7 days. Fruit stored at 5 °C lost ripening capacity even after transfer to 20 °C. Fruit stored at 2 and 10 °C did not ripen during 21 days storage, but ripened after transfer to 20 °C. However, these fruit rapidly lost water and exhibited browning discoloration. At 15 °C fruit ripened unevenly, possibly due to variability of harvest maturity. Fruit ripening either commenced at harvest time and continued during storage, or the fruit remained unripe. Fruit stored at 20 °C ripened normally, but rapidly lost quality due to ethanol accumulation and softening. Activities of superoxide dismutase (SOD), ascorbate peroxidase (APX), and catalase (CAT), enzymes directly related to ROS scavenging increased during storage at 20 °C, but had lowest values at 5 °C. Activities of dehydroascorbate reductase (DHAR), monodehydroascorbate reductase (MDHAR) and glutathione reductase (GR), enzymes, related to continual ascorbate oxidation and reduction, increased in fruit stored at 5 °C. The results indicate that at 5 °C, fruit have low capacity to scavenge SOD, which caused damage to the fruit and disturbed the ripening process. Nevertheless, storing carambola at 5 °C results in extended appearance life and therefore commercial acceptability, although may result in poor flavor quality due to chilling injury.