Department of Agronomy, University of Illinois, 1102 South Goodwin Ave., Urbana, Illinois 61801.
Plant Physiol. 1991 Apr;95(4):1106-12. doi: 10.1104/pp.95.4.1106.
Although isoflavonoids are known to be inducers of nod genes in Bradyrhizobium japonicum, it was recently proposed that internal root levels of isoflavonoids may be important in nodule development on soybean (Glycine max [L.] Merr.). The hypernodulating soybean mutants were shown to accumulate higher root concentrations of isoflavonoid compounds (daidzein, genistein, and coumestrol) and to be more extensively nodulated than was the Williams parent when inoculated with B. japonicum. The hypernodulating mutants and the parent line, Williams, also showed decreased isoflavonoid concentrations and decreased nodule development if N was applied. The current study evaluated the effect of localized NO(3) (-) application on root isoflavonoid concentration and on nodulation in split-root systems of the Williams wild type and a hypernodulating mutant (NOD1-3). Nitrate application markedly decreased isoflavonoid concentrations in non-inoculated soybean roots. When roots were inoculated, nodule number, weight, and nitrogenase activity were markedly suppressed on the root-half receiving 5 millimolar NO(3) (-) compared with the other root-half receiving 0 millimolar NO(3) (-). High performance liquid chromatographic analyses of root extracts showed that the root-half receiving 5 millimolar NO(3) (-) was markedly lower in isoflavonoid concentrations in both soybean lines. This was partially due to the localized stimulatory effect of NO(3) (-) on root growth. The inoculated NOD1-3 mutant had higher isoflavonoid concentrations than did the Williams control in both the presence and absence of NO(3) (-). These results provide evidence that the site of N application primarily controls the site of nodulation inhibition, possibly through decreasing isoflavonoid levels. Although the effect of NO(3) (-) on nodule development and root isoflavonoid concentration was strongly localized, there was evidence that NO(3) (-) also resulted in a systemic effect on root isoflavonoids. The results are consistent with previous speculation that internal levels of root isoflavonoids may affect nodule development.
虽然异黄酮被认为是诱导根瘤菌 Bradyrhizobium japonicum 结瘤基因的诱导物，但最近有人提出，大豆（Glycine max [L.] Merr.）根内的异黄酮水平可能对结瘤发育很重要。与接种根瘤菌的 Williams 亲本相比，超结瘤大豆突变体积累了更高的根异黄酮化合物（大豆苷元、染料木黄酮和香豆雌酚）浓度，并且结瘤更为广泛。当施用 N 时，超结瘤突变体和亲本系 Williams 的异黄酮浓度也降低，结瘤发育减少。本研究评估了局部施加 NO(3) (-) 对根异黄酮浓度和分根系统中 Williams 野生型和超结瘤突变体（NOD1-3）结瘤的影响。硝酸盐施加显著降低了未接种大豆根中的异黄酮浓度。当根系接种时，与接收 0 毫摩尔 NO(3) (-) 的另一半根系相比，接收 5 毫摩尔 NO(3) (-) 的根系的根结瘤数量、重量和固氮酶活性显著受到抑制。对根系提取物的高效液相色谱分析表明，在两种大豆品系中，接收 5 毫摩尔 NO(3) (-) 的根系异黄酮浓度明显较低。这部分是由于 NO(3) (-) 对根系生长的局部刺激作用。在有或没有 NO(3) (-) 的情况下，接种的 NOD1-3 突变体的异黄酮浓度均高于 Williams 对照。这些结果提供了证据，表明氮素施加的部位主要控制结瘤抑制的部位，可能是通过降低异黄酮水平。尽管 NO(3) (-) 对结瘤发育和根异黄酮浓度的影响具有很强的局部性，但有证据表明，NO(3) (-) 也对根异黄酮产生了系统性影响。结果与先前的推测一致，即根内异黄酮水平可能影响结瘤发育。
