Sa T M, Israel D W
Department of Soil Science, Plant Physiology Program, Box 7619 North Carolina State University, Raleigh, North Carolina 27695.
Plant Physiol. 1991 Nov;97(3):928-35. doi: 10.1104/pp.97.3.928.
Characterization of the effects of long-term P deficiency and of onset and recovery from P deficiency on bacteroid mass and number per unit nodule mass and energy status of soybean (Glycine max L. Merr.) nodules was used to investigate the mechanisms by which P deficiency decreases symbiotic N(2) fixation. The continuous P deficiency treatment (0.05 millimolar P) significantly decreased the whole plant dry mass, P, and N by 62, 90, and 78%, respectively, relative to the P-sufficient control (1.0 millimolar) at 44 days after transplanting. Specific nitrogenase activity was decreased an average of 28% over a 16-day experimental period by P deficiency. Whole nodules of P-deficient controls contained 70 to 75% lower ATP concentrations than nodules of P-sufficient controls. Energy charge and ATP concentrations in the bacteroid fraction of nodules were not significantly affected by P treatment. However, ATP and total adenylate concentrations and energy charge in the plant cell fraction of nodules were significantly decreased 91, 62, and 50%, respectively, by the P deficiency treatment. Specific nitrogenase activity, energy charge, and ATP concentration in the plant cell fraction increased to the levels of nonstressed controls within 2, 2, and 4 days, respectively, after alleviation of external P limitation, whereas bacteroid mass per unit nodule mass and bacteroid N concentration did not increase to the level of nonstressed controls until 7 days after alleviation of external P limitation. All of these parameters except bacteroid mass per unit nodule mass decreased to the levels of the P-deficient controls by 11 days after onset of external P limitation. Concentration of ATP in the bacteroid fraction was not significantly affected by alteration in the external P supply. Energy charge in the bacteroid fraction from plants recovering from P deficiency was decreased to a small (10%) but significant extent (P < 0.05) at two sampling dates relative to P-sufficient controls. These ATP concentration and energy charge measurements indicate that P deficiency impaired oxidative phosphorylation in the plant cell fraction of nodules to a much greater extent than in the bacteroids. The concurrence of significant changes in specific nitrogenase activity (2 days) and in the energy charge (2 days) and ATP concentration (4 days) in the plant cell fraction during recovery from external P limitation is consistent with the conclusion that P deficiency decreases the specific nitrogenase activity by inhibiting an energy-dependent reaction(s) in the plant cell fraction of the nodules.
通过对大豆（Glycine max L. Merr.）根瘤中类菌体质量、单位根瘤质量的类菌体数量以及能量状态进行长期磷缺乏影响、磷缺乏的起始和恢复的表征，来研究磷缺乏降低共生固氮作用的机制。与移栽后44天的磷充足对照（1.0毫摩尔）相比，持续磷缺乏处理（0.05毫摩尔磷）使整株植物干质量、磷和氮分别显著降低了62%、90%和78%。在16天的实验期内，磷缺乏使比固氮酶活性平均降低了28%。磷缺乏对照的整个根瘤中ATP浓度比磷充足对照的根瘤低70%至75%。根瘤类菌体部分的能荷和ATP浓度不受磷处理的显著影响。然而，磷缺乏处理使根瘤植物细胞部分的ATP、总腺苷酸浓度和能荷分别显著降低了91%、62%和50%。在外部磷限制解除后，植物细胞部分的比固氮酶活性、能荷和ATP浓度分别在2天、2天和4天内恢复到非胁迫对照的水平，而单位根瘤质量的类菌体质量和类菌体氮浓度直到外部磷限制解除7天后才恢复到非胁迫对照的水平。在外部磷限制开始11天后，除单位根瘤质量的类菌体质量外，所有这些参数都降至磷缺乏对照的水平。类菌体部分的ATP浓度不受外部磷供应变化的显著影响。与磷充足对照相比，在两个采样日期，从磷缺乏恢复的植物的类菌体部分的能荷降低了一小部分（10%）但显著（P < 0.05）。这些ATP浓度和能荷测量结果表明，磷缺乏对根瘤植物细胞部分氧化磷酸化的损害程度远大于对类菌体的损害。在从外部磷限制恢复过程中，植物细胞部分比固氮酶活性（2天）、能荷（2天）和ATP浓度（4天）的显著变化同时出现，这与磷缺乏通过抑制根瘤植物细胞部分的能量依赖反应来降低比固氮酶活性的结论一致。
