用试管-玻片培养技术研究铵对木麻黄根瘤形成的影响

Using the Test Tube-Sllde Method to Study the Effect of NH_4^+ on the Nodulation of Casuarina cunninghamiana

用植物试管玻片培养技术研究NH_4^+对细枝木麻黄及Frankia菌株Co01共生体系建立过程的影响。NH_4^+(100,150ppm(NH_4)_2SO_4)通过阻止菌株Cc01与其宿主细枝木麻黄根毛壁的亲和作用来影响结瘤。但NH_4^+不能阻抑菌株Cc01中结瘤基因pel和cel的表达及纤维素酶和果胶酶活性,且菌丝一旦侵入宿主皮层细胞,并形成根瘤原基及前根瘤,则NH_4^+(250ppm(NH_4)_2SO_4)就不再阻止原基进一步发育为成熟的根瘤。但在这种情况下,NH_4^+能抑制根瘤的固氮活性。

By using the test tube-slide method, modified by us, to culture theplants (Fig. 1), we studied the influence of NH_4^+ on the establishmentof Frankia strain Cc01 and C. cunninghamiana symbiotic system. The hyphase of the Frankia strain could stick tighly to the root hairs of the N-free seedlings after 24 h of inoculation (Plate. 1). However, medium dosage of NH_4^+ (100, 150 ppm (NH_4)_2SO_4) could inhibit the combination ability between the hyphae and the cell wall of root hairs, and affect the nodulation. The root hairs of the plants were much fewer when they grew with high dosage of NH_4^+ (250ppm (NH_4)_2SO_4). When the root hairs stimulated by the Frankia strain, had curled and deformed(Plate. 2),the further infection of the hvphae and nodulation couldn't be ceased by 100 ppm (NH_4)_2SO_4, but could be inhibited by 150 and 250 ppm (NH_4)_2SO_4. However, if the hyphae had infected into the roots and initiated the nodule primordia and formed prenodules (Plate. 5), the formation of nodules couldn't be ceased by the high-dosage of NH_4^+, but these nodules gave no nitrogenase activity (Table 1). NH_4^+ couldn't inhibit the expression of some nod genes, pel and cel, in the cells of strain Cc01 and couldn't influence both the activities of cellulase and pectinase either (Table 2). This sug gested that the nodulation can be inhibited by NH_4^+ influencing the metabolism of the roots of host plant.