| Preservation is one of the main tasks in citrus postharvest. In recent years, as people grow public concern on the health and environmental hazards, developing alternative approaches to control disease and maintain quality are needed in citrus industry. Sweating is one of traditional treatment widely used in China, heat treatment, as a postharvest treatment, was used in international community in the past decades. Both methods were proven to be effective on improving storage characteristics of Citrus. However, the mechanisms of both treatments on decay control remain poorly realized. In present study, the respiration rate, total soluble solids and disease tolerance in Citrus unshiu Marc. cv. Kamei were measured among the fruit via sweating or heat treatment respectivately. To explore the mechanisms to both sweeting and heat treatments at the proteomic level,2-D PAGE analyses were carried out. The main results were as follws:1. No obvious changes on fruit quality resulted from sweating or heat treatment. The parameters of weight loss, respiration rate, and total soluble solids of fruit were measured after both treatments and subsequent storage. The results demonstrated that no obvious changes on fruit quality caused by either treatment.2. Sweating or heat treatment can increase fruit resistance against Penicillium italicum. Inoculation experiments demonstrated that fruit treated via sweating or heat treatment have lower disease incidences than the control on the initial day of visualable symptom and samller lesion diameter during the disease process.3. Sweating or heat treatment can induced the activity of antioxidant enzymes. The experiments showed that the activity of phenylalanine ammonia (PAL) and superoxide dismutase (SOD) were induced up-regulating by sweating or heat treatments. While, H2O2 content in treated fruit was lower than that of the control after 12 and 21 days of treatments.4. Sweating or heat treatment stimulated significant changes on expression of proteins. After 2-DE analyzing, changes in spot intensity between treated and control fruit samples were quantified using the ImageMaster 2D Platinum 5.0 software. The results showed than at the 95% level, there were 50 significantly different spots between treatments and control. A total of 50 differentially expressed protein spots were analyzed by the MALDI-TOF/TOF, and 34 sopts were successfully identified. Functions of all these identified proteins were involved in metabolism and energy pathway (38%), defense and stress response (35%), protein synthesis, modification and degradation (12%), transporters (6%), cell structure (3%), and others (12%). The results demonstrated that sweating or heat treatment can induced the expression of defense and stress response proteins.5. Sweating or heat treatment may induce systemic acquired resistance, and result in the improvement of fruit storage property. Defense and stress response related genes in peel, including superoxide dismutase (SOD), ascorbate peroxidase (APX), beta-1,3-glucanase (GLU), high molecular weight heat shock protein (HSP), abscisic stress ripening-like protein (ASR), isoflavone reductase-like protein were analyzed at the expression level by real-time RT-PCR, the results revealed that the expression of defense and stress response genes might be triggered by both treatments. This is consistent with proteomic analysis6. Both common and distinctive mechanisms involved in sweating or heat treatment. Our results showed that sweating treatment could induce the expression of superoxide dismutase, ascorbate peroxidase and high molecular weight heat shock protein. While, heat treatment could specifically regulate the expression of beta-1,3-glucanase, effect the distribution of H2O2, and increase the content of SA in the peel. However, chitinase class 3, lipocalin proteins and isoflavone reductase-like proteins were regulated by both treatments. |
PDF Full Text Request