台湾相思结瘤固氮与吸氢酶活性研究

台湾相思的根系具有多年生的根瘤,根瘤初发生时球状,以后发育成分叉瘤和扇状瘤。根瘤固氮活性因苗龄、成熟度不同而有明显差异。环境条件影响结瘤及固氮活性。15℃时结瘤受到明显抑制,固氮作用最适温度条件是25～30℃。光照不足降低根瘤固氮活性。短期轻度干旱不影响根瘤固氮活性,但持续干旱使固氮活性明显下降。pH4.5～8.5条件能正常结瘤,pH5.5时结瘤最好。根瘤固氮作用时不释放H_2,具有较高的吸氢酶活性,在固氮反应系统中加入5％的H_2,能提高根瘤固氮活性。

Symbiotic Nitrogen-fixing and Uptake Hydrogenase Activity in Acacia confusa

Acacia confusa is an important fuelwood tree in South China. Their root systems bear perennial nodules. The nodules change considerably in external shape as their growth, from single sphere to branchy or multibranchy. The level of nitrogenase activity, as determined by acetylene reduction assay, markedly varied with the age and physiological stages of nodules. Effect of environmental factors on nodulation and nitrogen fixation of A. confusa was investigated. The optimum temperature for nitrogenase activity of nodules ranged 25-30C , low temperature of 15 C seriously retarded nodulation. Shading reduced nitrogenase activity of nodules. Minor soil water deficit did not affect the acetylene-reducing activity, but serious soil drought markedly reduced the activity of nitrogen fixation. In nitrogen-free culture solution with a pH between 4. 5 and 8.5, roots of seedling normally nodulated and at pH 5. 5,thenumber of nodules per plant was the most. Expression of uptake hydrogenase activity was found in nodules of A. confusa. When adding 5% molecular hydrogen to reaction system, nitrogenase activity in nodules increased markedly.