Molecular Mechanism Of Citrus Fruit Storage Period Prolonged By Postharvest Physical Treatments

Citrus fruits, from harvest to human consumption, it require a length storage period for postharvest treating, storing, shipping and marketing. During that time, the main damages of fruit are coming from physiological disorders, pathogenic disease and mechanical damage. As more attention was paid in food safety and environmental pollution, postharvest physical treatment become into the first choice instead of chemical treatments. Postharvest physical treatments are used to inhibit fruit pathogens, reduce fruit weight loss and increase fruit resistibility during postharvest storage, containing bagging, sweating, heat treatment, cold storage, gas controlling storage, and so on. However, less information about the mechanism is available. Along with the technological progress of proteomics, transcriptomics and metabolomics, high-throughput analysis technology provide important theoretical basis for understanding the regulatory mechanism of postharvest physical treatment induced citrus fruit resistance. In present study, ponkan (C. reticulata cv. Egan No.1) fruits, Hirado Buntan pummelo (HBP; Citrus grandis x C. paradis) fruits and'Kamei'Satsuma mandarin(Citrus unshiu Marc. Guoqing No.1) fruits were chosen to explore the mechanisms of postharvest treatments induced fruit resistibility and delayed fruit senescence during postharvest storage. Main results were following.1. Comparative proteomics analysis was carried out in'Egan No.1'ponkan fruit at differential storage periods. Two-dimensional gel electrophoresis (2-DE) coupled Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) were performed to examine the protein changes during the postharvest storage period. Results showed that74proteins were differentially regulated, from which56proteins were identified by blasting against NCBInr (green plant) and EST viridiplantae databases. All identified proteins were then classified into functional classes according to known biosynthetic pathways, including C-compound and carbohydrate metabolism, amino acid metabolism and response to storage environmental stimuli. In addition, subcellular location and time-dependent accumulation trends of differentially accumulated proteins associated with fruit quality were analyzed. The result showed Fructose kinase, citrate synthase, aconitase and malic dehydrogenase play key role in fruit quality regulation during storage.2. HBP fruit were chosen to explore the mechanisms that maintain citrus fruit quality during lengthy LT storage using transcriptome and proteome studies based on digital gene expression (DGE) profiling and2-DE, respectively. This study showed that LT up-regulated stress-responsive genes and arrested signal transduction, primary metabolism, secondary metabolism and the transportation of metabolites. Calcineurin B-like protein (CBL)-CBL-interacting protein kinase (CBL-CIPK) complexes might be involved in the signal transduction of LT stress. In addition, the accumulation of limonin, nomilin, methanol and aldehyde, as well as the up-regulated heat shock proteins,14-3-3protein, COR15and cold response-related genes provided a comprehensive proteomics and transcriptomics view on the coordination of fruit low temperature stress responses. Fruit quality is likely to be regulated by sugar-mediated auxin and abscisic acid signaling, such as down-regulation of carbohydrate metabolism, nitrogen metabolism, lipid metabolism and secondary metabolism.3.'Kamei'Satsuma mandarin fruits were chosen to explore the mechanisms of HT induced fruit resistibility during postharvest storage using metabolome studies based on Gas chromatography coupled to mass spectrometry (GC-MS), High performance liquid chromatography hybrid quadrupole time-of-flight mass spectrometry (HPLC-QTOF-MS). This study has provided new insights into HT induced fruit resistance. Interpretation of the data for metabolites revealed that reactive oxygen species (ROS) was paly a vital role in HT fruit stress resistance. The intracellular H2O2content was decreased in HT fruits, which might increase fruit resistibility in response to external stress. In addition, Flavonoids were up-regulated in HT fruits, which directly involved in the response to external stress. Moreover, the decreased H2O2was used for synthesis of lignin, which lead to the content of lignin was increased in HT fruits. The increased lignin thickened cell wall, which was involved in isolated external pathogens from fruits.4.'Kamei'Satsuma mandarin fruits were chosen to explore the mechanisms of ST induced fruit resistibility during postharvest storage using metabolome studies based on GC-MS and LC/QTOF-MS. This study has provided new insights into ST induced fruit resistance. Interpretation of the data for metabolites revealed that salicylic acid (SA) was paly a vital role in ST fruit stress resistance. Many metabolites were up-accumulated in ST pericarp, such as sugars (except arabinose), organic acids (except Hydroxypyruvic acid), fatty acids, sugar alcohols, and other acids. All those changes in metabolites were correlated well in SA treated pericarp.