McClure P R, Israel D W
Department of Soil Science and United States Department of Agriculture, Science and Education Administration, Agricultural Research, Department of Soil Science, North Carolina State University, Raleigh, North Carolina 27650.
Plant Physiol. 1979 Sep;64(3):411-6. doi: 10.1104/pp.64.3.411.
Experiments were conducted to characterize the distribution of N compounds in the xylem sap of nodulated and nonnodulated soybean plants through development and to determine the effects of exogenous N on the distribution of N compounds in the xylem. Xylem sap was collected from nodulated and nonnodulated greenhouse-grown soybean plants (Glycine max [L.] Merr. "Ransom") from the vegetative phase to the pod-filling phase. The sum of the nitrogen in the amino acid, nitrate, ureide (allantoic acid and allantoin), and ammonium fractions of the sap from both types of plants agreed closely with total N as assayed by a Kjeldahl technique. Sap from nodulated plants supplied with N-free nutrient solution contained seasonal averages of 78 and 20% of the total N as ureide-N and amino acid-N, respectively. Sap from nonnodulated plants supplied with a 20 millimolar KNO(3) nutrient solution contained seasonal averages of 6, 36, and 58% of total N as ureide-N, amino acid-N, and nitrate-N, respectively. Allantoic acid was the predominant ureide in the xylem sap and asparagine was the predominant amino acid. When well nodulated plants were supplied with 20 millimolar KNO(3), beginning at 65 days, C(2)H(2) reduction (N(2) fixation) decreased relative to nontreated plants and there was a concomitant decrease in the ureide content of the sap. A positive correlation (r = 0.89) was found between the ureide levels in xylem sap and nodule dry weights when either exogenous nitrate-N or urea-N was supplied at 10 and 20 millimolar concentrations to inoculated plants. The results demonstrate that ureides play a dominant role in N transport in nodulated soybeans and that the synthesis of ureides is largely dependent upon nodulation and N(2) fixation.
开展实验以表征结瘤和未结瘤大豆植株木质部汁液中氮化合物在整个生长发育过程中的分布情况，并确定外源氮对木质部中氮化合物分布的影响。从营养生长阶段到结荚期，采集温室种植的结瘤和未结瘤大豆植株（大豆[Glycine max (L.) Merr. “Ransom”]）的木质部汁液。两种植株汁液中氨基酸态氮、硝态氮、酰脲（尿囊酸和尿囊素）和铵态氮的氮含量总和与凯氏定氮法测定的总氮量非常接近。供应无氮营养液的结瘤植株汁液中，酰脲态氮和氨基酸态氮分别占总氮量的季节性平均值为78%和20%。供应20毫摩尔硝酸钾营养液的未结瘤植株汁液中，酰脲态氮、氨基酸态氮和硝态氮分别占总氮量的季节性平均值为6%、36%和58%。尿囊酸是木质部汁液中主要的酰脲，天冬酰胺是主要的氨基酸。当在65天时开始给结瘤良好的植株供应20毫摩尔硝酸钾时，相对于未处理植株，乙炔还原（固氮）作用降低，同时汁液中酰脲含量也随之降低。当以10和20毫摩尔浓度向接种植株供应外源硝态氮或尿素氮时，木质部汁液中酰脲水平与根瘤干重之间呈正相关（r = 0.89）。结果表明，酰脲在结瘤大豆的氮转运中起主导作用，且酰脲的合成很大程度上依赖于结瘤和固氮作用。
