MORPHOLOGICAL ANALYSIS ON THE MECHANISM OF NITRATE-INHIBITION OF ROOT NODULE FORMATION IN SOME LEGUMES ASSOCIATED WITH DIFFERENT RHIZOBIA

硝酸盐对根瘤形成初期的抑制作用。采用玻片培养法和生长袋培养法对长喙猪屎豆和猪屎豆进行了研究。研究结果如下：1. In S.根、根瘤的形成受硝酸盐浓度的影响。接种后7天，在5 mM硝酸盐的存在下，根瘤的数量最低，在0 mM时最高。5 mM硝酸盐显著减少侧根的数量。此处理还抑制根瘤菌附着到根表面，通过X-Gluc染色检测到根表面上的蓝色区域。在树脂包埋切片中观察到侧根组织中根瘤原基的形成。对琼脂包埋切片的观察表明，在5 mM硝酸盐存在下，结核的发育肯定会延迟。硝酸盐对生长袋中生长的两种猪屎豆根瘤形成和固氮酶活性有抑制作用。结果表明，在相同的生长条件下，根的干重、表面积和总长度均高于对照。10 mMN的硝酸盐处理也抑制了根瘤的形成，表明硝酸盐通过抑制根系生长抑制根瘤的形成.显微镜载玻片或生长袋培养技术可方便地阐明供试豆科植物根系结构与根瘤形成之间的抑制关系。对根瘤菌侵染过程和硝酸盐抑制作用的机理的研究正在进行中。

Inhibitory effects of nitrate on initial stages of root nodule formation in S. rostrata and Crotalaria sp. were investigated by using a microscope slide culture method and a growth pouch culture method. The results are summarized as follows ;1. In S. rostrata, formation of root, nodules was affected by the nitrate concentration. Seven days after Inoculating, the number of nodules were the lowest in the presence of nitrate at 5 mM, and the highest at 0 mM. Nitrate applied at 5 mM markedly reduced the number of lateral roots. This treatment also inhibited rhizobial attachment to the root surface, on which the blue colored area was detected by X-Gluc staining. Formation of root nodule primodia in the lateral root tissue was observed in resin-embedded sections. Observations of the agar-embedded sections revealed that the nodule development was definitely delayed in the presence of nitrate at 5 mM.2. Root nodule formation and nitrogenase activity in two species of Crotalaria grown in a growth pouch were inhibited by application of nitrate to culture solution. Dry weight, surface areas, and total length of the roots of C. spectabilis were also reduced by application of nitrate at 10 mMN, suggesting that nitrate inhibited root nodule formation through reduction of the root growth.3. The culture techniques with a microscope slide or a growth pouch might be rather convenient to clarify the inhibitory relationship between the structure of root system and nodule formation in the tested legume species. Further investigation of the mechanisms on the rhizobia-infection process and inhibitory effect of nitrate is now in progress.