|TORRES, CAROLINA - UNIVERSITY OF TALCA|
|HERNANDEZ, OMAR - UNIVERSITY OF TALCA|
|MYOA-LEÓN, MARIA - UNIVERSITY OF TALCA|
|RAZMILIC, IVAN - UNIVERSITY OF TALCA|
Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/24/2016
Publication Date: 8/4/2016
Citation: Torres, C.A., Hernandez, O., Myoa-León, M.A., Razmilic, I., Rudell Jr, D.R. 2016. Antioxidant metabolism and gene expression during ‘‘stain’’ development on ‘Fuji’ apples during cold storage. HortScience. 51(8):1031–1037.
Interpretive Summary: Incidence of light stress-related postharvest disorders contributes to significant annual losses of multiple apple cultivars. It is well-established that high light and heat prior to harvest are responsible for the development of stain during cold storage. Prior studies have focused on peel chemistry associated with high light during the growing season. Less is known about changes occurring in peel subjected to these conditions in combination with the stresses imposed by chilling during cold storage. Here, we have identified a number of biochemical systems in apple peel that are associated with the postharvest manifestation of heat and solar stress during the growing season. Changes could be exploited to develop improved phenotyping and risk assessment tools.
Technical Abstract: A distinct type of postharvest skin browning of apple fruit called ‘stain’ is a frequent disorder of ‘Fuji’ apples grown under high light conditions. Symptoms typically develop only on sun-exposed regions of the peel regardless of the presence of prior sun-related injury, but usually on the margins of the most exposed areas. The role of different antioxidant systems in tissue exposed to different levels of sunlight and having different degrees of sun-related injury already present were investigated during cold storage (1°C, >90%RH). Ascorbic acid (AsA) and glutathione (GSH) concentrations, AsA-GSH recycling enzymes activities and gene expression, and flavonoids and carotenoid concentrations were determined every 30 days. ‘Stain’ incidence increased with sun exposure and sunburn level. Fruit peel without sunburn symptoms (shaded and sun-exposed) had the highest ascorbic acid (AsA) content. The AsA-GSH recycling enzyme activities and gene expression levels had no clear relationship with sun exposure during cold storage. Chlorophyll a and b levels diminished over time and were higher in tissue without any type of sun injury. In contrast, carotenoid levels increased as sun injury incidence increased and remained relatively stable during storage. Total phenolics and quercetin glycosides levels changed coincidently during storage. Results indicate that the AsA-GSH cycle does not play a direct role in ‘Fuji’ ‘stain’ development. Nevertheless, reduced ascorbate levels may reduce the capacity to prevent oxidative stress provoked damage which may, in turn, may result in oxidation of quercetin glycosides, then, skin browning. Stain and sunscald appear to be the same disorder but in two different apple genotypes.