Proteomic Changes Of Cd Stress Response In Kandelia Candel Roots And Analysis Of Differentially Expressed Proteins

With the development of modern industry and the increasing human activity, heavy metal pollution of the environment has become a major risk. Cadmium (Cd) is a relatively rare heavy metal elements, human activities in various ways may bring about cadmium into the soil and water. Mangrove ecosystems, possessing great ecological and commercial value, are diverse communities in intertidal zones of tropical and subtropical coastal rivers, estuaries and bays. Heavy metals are common pollutants in urban aquatic ecosystems and are one of the main anthropogenic toxic compounds found in polluted mangrove locales. Mangroves appear to possess a great tolerance to relatively high levels of heavy metal pollution. Kandelia candel is major mangrove specie of the eastern group and is dominant along South China coast. To study the cadmium tolerance mechanism of Cd is of great significance and wide application prospects.This work focuses on proteomic responses in roots of cadmium exposed K. candel plants. To complement the proteomic results, several enzymatic activity assays were also carried out, to gain further insight in the mechanism behind cadmium stress response. The main results were as follows.1.Effect of different content Cd(0,100,200,400,800μM) on Kandelia candel at 72h were studied. We determined the activity of SOD,POD,CAT,APX,GR and the content of AsA,GSH,proline. The results showed:Low content Cd stress (100-400μM) increased the activity of SOD, POD, APX, GR, CAT and the content of ASA, GSH, proline. This may showed that roots of K. candel increased antioxidant capacity in order to ease the damage caused by Cd stress.However, during high concentration Cd stress (800μM), the antioxidant defense system is also correspondingly weakened.2. Optimized technical system of two-dimensional electrophoresis (2-DE) including pH range, technical parameters in IEF and the protein extraction methods were screeded.A 2-DE system was finally set up for proteomic research of Kandelia candel. 3.Protein expression in Kandelia candel roots in response to Cd stress was analysed by 2-DE using 4 to 7 pH gradient IPG strips (24 cm) and 12.5% polyacrylamide gels. Approximately 1,000 separated protein spots were visualized on 2-DE gel by CBB R-250 staining. To obtain detailed information about the proteome changes, we digitized and analyzed using PDQuest software. The quantitative image analysis revealed that 55 protein spots were differentially expressed with 1.5 fold abundance change. These 55 proteins were analyzed by using MALDI-TOF-MS/MS. The mass spectra obtained from MALDI-TOF-MS/MS were searched in the NCBI database by using the Mascot search engine. 53 proteins were identified successfully. Functional annotation of the identified proteins was carried out to subdivide proteins into 6 groups based on their functional categories, including:protein metabolism (protein folding, protein synthesis, and proteolysis) related proteins, amino acid transport and metabolism related proteins, energy and carbohydrate metabolism, detoxifying and antioxidation, signal transduction and others proteins.By combining protein function, metabolic pathway and the physiological results, we illustrated one physiological and chemical pathway of Kandelia candel in responses to Cd stress. Under Cd stress, the redox homeostasis in plants was wrecked and caused results in oxidative burst, which in turn caused damages to cellular component and may influence a series of physiological pathways, such as proteolysis and amino acid metabolism. Membrance system may also be affected by oxyradical. In order to resist Cd stress, proteins involved in detoxifying and antioxidation were up-expressed. The antioxidant enzymes effectively cleared ROS molecules, such as hydrogen peroxide, superoxide anions,protecting the cell membrance system.Secondly, the Cd stress launched a series of plants defense mechanism to maintain and repair the damaged balance in root cells. Finally, regulation of signaling networks, such as up-regulated expression of 14-3-3 protein, was strengthened to enhance the stress signal induction and a normal physiological state.