| Melon (Cucumis melo L.) is a typical hypoxic-sensitive plant. But the yield and quality of melon often reduced by lacking of oxygen in the rhizosphere according to soil compaction, irrigation excessive, low dissolved oxygen concentration of nutrient solution in soilless culture and the root mat formation, which has become the decisive obstacles to large-scale development of melon production. In this paper, hydroponic experiments were performed to investigate the effects of exogenousγ-aminobutyric acid (GABA) application on polyamine metabolism and comparative proteomics of root total proteins in seedlings of melon cultivar‘Xiyu No.1’under hypoxia stress, which clarified the possible mechanisms of GABA enhancing hypoxia-tolerance in melon through metabolomics and proteomics technology.The main results were presented as follows:1. Hypoxia stress induced a significant increase in polyamines contents, polyamines of free form had higher content but lower content of bound form in leaves and roots of melon seedlings, the content sequence of PAs in roots was Put>Spd>Spm, and in leaves was Spd>Put>Spm. The three forms Spd and Spm contents in leaves were higher than that in roots, but Put contents were lower. Exogenous GABA significantly increased the contents of Put, Spd and Spm. However, simultaneously applying GABA and VGB could significantly decreased the content of PAs under hypoxia stress.2. Hypoxia stress induced a significant increase in activities of polyamine synthesis in melon seedlings, especially the change in roots, activities of polyamine synthesis in roots fallen sharply after reached maximum in 4 days, but maintained stable of ADC and SAMDC activities in leaves after reached maxmum. Compare with hypoxia treatment, exogenous GABA significantly increased the activities of ADC, ODC and SAMDC both in roots and in leaves.3. Compared with normoxic treatment, the activities of PBS-extractable form and cell-wall-bound form polyamine oxidase enzymes were higher in melon roots and in leaves under hypoxia stress; The activities of cell-wall-bound form DAO and PAO in roots were lower than in leaves, while the activities of PBS-extractable form DAO and PAO were higher than in leaves. Compared with hypoxia stress treatment, exogenous GABA significantly decreased the act ivies of DAO and PAO.4. We selected and established a system for separation and analysis the melon root protein. Three improved methods were adopted to extract total protein,and which were analyzed and compared with each other, the results showed that TCA/acetone precipitation and SDS/phenol extraction had lower protein contents, more bands and spots could be detected on SDS gels and 2-DE gels by SDS/phenol extraction and Tris/phenol extraction-methanol/ammonium acetate precipitation, while TCA/acetone precipitation got the minimum spots and lost much of basic proteins.5. Comparative proteomics analysis of melon root total proteins have been preformed after 4 days treatment, we found proteomics of the four treatments in melon root had some obvious changes. Employing computer analysis, and the result indicated that valid protein spots in gels of hypoxia and hypoxia+GABA treatments were significantly increased. Between normoxic treatment and normoxic+GABA treatment, there were 54 differential protein spots. Compared with normoxic and hypoxia treatments, 62 significant differential protein spots were detected in the images. And 45 differential protein spots were detected in images of hypoxia treatment and hypoxia+GABA treatment. In this paper, 13 extremely significant differential protein spots have been chosen to identify by MALDI-TOF/TOF Mass Spectrometry, and the identified proteins include some plant anti-versus relative proteins such as glutathione transferase, ferrodoxin NADP oxidoreductase, cytosolic phosphoglycerate kinase and so on. But there were 4 spots have not high identification rate by mass spectrometry, and these proteins need further study when a prefect database has established. |
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