| Cassava(Manihot esculenta Crantz) belongs to Manihot genus of Euphorbiaceae. Because of its adaptabilities, high resistances to drought and infertile soil, high biomass and starch content, cassava is the main staple food for700million people who live in the tropics and subtropics areas. It is also used to be important resources of starch processing and bio-energy production. Due to the small area of tropics in China, the uninterrupted increase of the requirements of cassava, so planting in the northern area is an important direction for developing cassava industry. But cassava is very sensitive to low temperature, the responses on the physiological and biochemical activities to low temperature and proteome analysis will be conducted in the present study. It would be helpful to understand the cold resistance mechanism of cassava, and providing a new way to screening for cold resistant cassava germplasms.The physiological and biochemical methods and proteomics technology will be used in the present study. Tssue culture plantlets of cassava cultivar SC8and Co11046introduced from CIAT, Colombia were used as research materials. The dynamic changes of leave physiological and biochemical characteristics of cassava plantlets exposed to low temperature (5℃) for15days and the expressions of global proteins in cassava leave exposed to5℃for10days were analyzed.The results are as follows:1. Under low temperature stress, chlorophyll content of SC8and Co11046have shown a gradually decrease, and content of chlorophyll a declined slowly, while chlorophyll b decreased rapidly. The decline level of chlorophyll content in Co11046was more than SC8. Relative electrical conductivity (REC) was also enhanced with increased-stress level; the results showed that cell membrane of Col1046was more sensitive to continuous low temperature. The effects of low temperature on MDA were mainly shown at the late period of treatment, the content of MDA rises steadily after7days, while rise rapidly after10days. The content of soluble sugar (SS) and free proline in two varieties were gradually increased until reach a certain level, and then has a downward trend, but their contents were higher than that of control. In the early period of low temperature stress, the activities of two enzymes increased rapidly, SOD activity has always maintained a high level until10days later, the activity decreased rapidly, and below the control level after15days. POD activity reached at peak point and then gradually decreased, but it always maintain at a relatively high level.2. The correlation analysis of7physiological and biochemical characteristics showed that chlorophyll content was negatively correlated with REC, proline content, MDA content, soluble sugar content and the activity of SOD and POD, and significantly negatively with relative conductivity, MDA content and soluble sugar content; Relative electrical conductivity was significantly positively related with proline and MDA content; SOD activity and POD activity showed a significant positive correlation. The principal component (PC) analysis showed that the eigenvalue (EV) and cumulate contribution (CC) rates in first PC, decided by REC, chlorophyll content and MDA content, were3.330and47.5%, respectively; the EV and CC in second PC consisting of activities of SOD and POD and SS were2.249and32.13%, respectively. The EV and CC in the third PC decided by free proline were0.869and12.42%, respectively. It seems to show that REC, chlopophyll content and MDA are the most important physiological and biochemical indexes for determining cold resistant abilities of cassava.3.45differential protein spots were in response to low temperature stress seen in2-DE images of the SC8leave, in which5up-regulated spots and20down-regulated spots were included. Of which32were successfully identified using MALDI-TOF-TOF-MS/MS; while in Co11046leaves,44differential protein spots were found, including10up-regulated spots and34down-regulated spots, of which33were successfully identified. These differential proteins participated in the pathways of photosynthesis, carbon metabolism and energy metabolism, protein synthesis, defense, and et al.4. Compared with differential proteins in the leave of SC8and Co11046,20proteins identified were the same and showed the same expression pattern. They are mainly related to photosynthesis, carbon metabolism and energy metabolism, protein synthesis, amino acid metabolism, signal transduction, cytoskeletal proteins, chaperones, cellular defense, antioxidant and DNA-binding proteins, in which40%were related with photosynthesis. This study was used to investigate the correlation of high photosynthesis efficiency and low temperature stress in global protein levels and will be helpful to screen high resistant cassava varieties under cold stress. |
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