Singleton P W, Bohlool B B
University of Hawaii, Honolulu, Hawaii 96822.
Plant Physiol. 1984 Jan;74(1):72-6. doi: 10.1104/pp.74.1.72.
A split-root growth system was employed to evaluate the effect of NaCl on nodule formation by soybean (Glycine max L. Merr. cv Davis). By applying the salinity stress and rhizobial inoculum to only one-half the root system, the effects of salinity on shoot growth were eliminated in the nodulation process. Rhizobium colonization of inoculated root surfaces was not affected by the salt treatments (0.0, 26.6, 53.2, and 79.9 millimolar NaCl). While shoot dry weight remained unaffected by the treatments, total shoot N declined from 1.26 grams N per pot at 0.0 millimolar NaCl to 0.44 grams N per pot at 79.9 millimolar NaCl. The concentration of N in the shoot decreased from 3.75% N (0.0 millimolar NaCl) to 1.26% N at 79.9 millimolar NaCl. The decrease in shoot N was attributed to a sharp reduction in nodule number and dry weight. Nodule number and weight were reduced by approximately 50% at 26.6 millimolar NaCl, and by more than 90% at 53.2 and 79.9 millimolar NaCl. Nodule development, as evidenced by the average weight of a nodule, was not as greatly affected by salt as was nodule number. Total nitrogenase activity (C(2)H(2) reduction) decreased proportionally in relation to nodule number and dry weight. Specific nitrogenase activity, however, was less affected by salinity and was not depressed significantly until 79.9 millimolar NaCl. In a second experiment, isolates of Rhizobium japonicum from nodules formed at 79.9 millimolar NaCl did not increase nodulation of roots under salt stress compared to nodule isolates from normal media (0.0 millimolar NaCl). Salt was applied (53.2 millimolar NaCl) to half root systems at 0, 4, 12, and 96 hours from inoculation in a third experiment. By delaying the application of salt for 12 hours, an increase in nodule number, nodule weight, and shoot N was observed. Nodule formation in the 12- and 96-hour treatments was, however, lower than the control. The early steps in nodule initiation are, therefore, extremely sensitive to even low concentrations of NaCl. The sensitivity is not related to rhizobial survival and is probably due to the salt sensitivity of root infection sites.
采用分根生长系统来评估氯化钠对大豆（Glycine max L. Merr. cv Davis）根瘤形成的影响。通过仅对根系的一半施加盐分胁迫和接种根瘤菌，在根瘤形成过程中消除了盐分对地上部生长的影响。接种根表面的根瘤菌定殖不受盐分处理（0.0、26.6、53.2和79.9毫摩尔氯化钠）的影响。虽然地上部干重不受处理影响，但地上部总氮含量从0.0毫摩尔氯化钠时的每盆1.26克氮降至79.9毫摩尔氯化钠时的每盆0.44克氮。地上部氮浓度从3.75%氮（0.0毫摩尔氯化钠）降至79.9毫摩尔氯化钠时的1.26%氮。地上部氮含量的降低归因于根瘤数量和干重的急剧减少。在26.6毫摩尔氯化钠时，根瘤数量和重量减少了约50%，在53.2和79.9毫摩尔氯化钠时减少了90%以上。以单个根瘤的平均重量为证据，根瘤发育受盐分的影响不如根瘤数量大。总固氮酶活性（C₂H₂还原）与根瘤数量和干重成比例下降。然而，比固氮酶活性受盐分影响较小，直到79.9毫摩尔氯化钠时才显著降低。在第二个实验中，与从正常培养基（0.0毫摩尔氯化钠）形成的根瘤中分离的根瘤菌相比，从79.9毫摩尔氯化钠条件下形成的根瘤中分离的日本根瘤菌菌株在盐分胁迫下并没有增加根瘤的形成。在第三个实验中，在接种后0、4、12和96小时对根系的一半施加盐分（53.2毫摩尔氯化钠）。通过将盐分施加延迟12小时，观察到根瘤数量、根瘤重量和地上部氮含量增加。然而，12小时和96小时处理中的根瘤形成低于对照。因此，根瘤起始的早期步骤对即使是低浓度的氯化钠也极其敏感。这种敏感性与根瘤菌的存活无关，可能是由于根感染部位对盐分敏感所致。
