| Myrica rubra Sieb. et Zucc (Chinese tree berry, red bayberry) is an important native fruit representing endemic species of China , is a tropical and subtropical fruit and is also a pioneer plant in Southern China. The root of M. rubra can fix nitrogen from atmosphere for plant growth in symbiosis with Frankia. It has extensive adaptability of cultivation andean easily be grown on barren lands with harsh environments and its trees have remarkable ecological effects which can increase water and soil conservation capability, adjust the climate of micro-environment, effectively control water flow and soil erosion, and decrease flood disaster. The trees of M. rubra also have a better fire resistibility to prevent fire from expanding. M. rubra is an ideal selection among the trees for soil conservation and forest ranges and has been selected as one kind of ecological tree by China National Forestry Bureau. With the adjustment of production structure and integrative development at mountainous regions, the area ofM.rubra has been increasing rapidly and M.rubra has been an important source of income for mountainous people.Nitrogen fixation is probably the second most important biochemical pathway after CO2 fixation on the earth. Biological nitrogen fixation is an important approach to solve lots of problems about population, food, energy and environment. It is more important for sustainable agriculture development to make full use of nitrogen fixation characteristics of M.rubra and how to exploit its economic and ecological benefits. Symbiotic nitrogen fixation,however, has less been reported. In order to exploit and develop efficiently symbiotic nitrogen fixation characteristics of M.rubra, the root nodules and its Frankia were studied thoroughly in the dissertation and the main results were summarized as followed./. Isolation and Identification of symbiotic nitrogen-fixing actinomycete from Myrica rubra root nodules Frankia strains were successfully isolated from M. rubra root nodules using Q++ and J-A solid media. Colonies of isolates on Q + + solid medium showed different colors and Gram-positive. Mycelia of the isolates are branched .septate and filamentous hypha about 0.6-1.1 μ m in diameter. The tip of hypha swells to form vesicle and these vesicles are eiher septate or non-septate, spherical and about 1.7~2.2 μ m in diameter. Sporangia of these isolates are pear-like or oval .about 15~30 μ m in diameter and spores are round , 1.4~1.7 μ m in diameter. The Frankia isolates grown in N-deficient BAP medium had acetylene reducing activities.2. Cultural characteristics of Frankia The cultural characteristics, and effects of carbon and nitrogen sources, pH, temperature on three Frankia strains were studied by microscopic examination and protein content detected by modified Bradford method. The results showed that BAP(nitrogen) solid media , BM+NZ and FMS liquid media are well suitable for the growth of Frankia MFC 11,MFC 12 and MPA11. They grow very well on BAP media with glucose .sodium pyruvate and Tween-80 as sole carbon source respectively and casamino acid or yeast extract as sole nitrogen source. They could use sodium propionate, but insufficiently. Urea could not be utilized. pH 5.5~ 6.5 were suitable for the growth of Frankia strain Mpcll and Mpall which were inhibited at pH above 7.0. Frankia MFC 11 grows normal under a temperature range of 25℃-33℃. The colors and morphologies of colonies, colors of mycelia and growth rates of different Frankia strains may be changed with the media types and cultural days.3. Heavy metal and antibiotic resistance of Frankia strains from root nodule of Myrica rubr The resistance of 10 Frankia strains to 9 kinds of heavy metals was determined by a growth inhibitionassay. In general, all of the strains were sensitive to low concentrations(<0.5 mmol/L= of Hg2+ and Ag+,but most of the strains were less sensitive to Pb2+ (5-10 mmol/L Cr2O72-(5-10 mmol/L) and AsO2- (5-10 mmol/L) while some of the strains were also less sensitive to Cu2+ Co2+ Ni2+...
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