Shelp B J, Da Silva M C
Department of Horticultural Science, University of Guelph, Guelph, Ontario Canada N1G 2W1.
Plant Physiol. 1990 Dec;94(4):1505-11. doi: 10.1104/pp.94.4.1505.
Pulse-chase feeding (30-120 minutes) of (14)C-labeled nitrogenous compounds to cut transpiring shoots was used to investigate the early fate of the major xylem-borne solutes in N(2)-fixing soybean (Glycine max) plants at the V(4) growth stage. By comparison with the foliar distribution of [(14)C]inulin (a xylem marker), it was determined that the phloem supply of allantoin, allantoic acid, asparagine, glutamine, aspartate, and arginine, respectively, provided about 20, 10, three, two, five, and 20 times the (14)C delivered to the developing trifoliolate in the xylem stream. Recovery of unmetabolized asparagine, aspartate, and arginine in this indicator trifoliolate, and significant declines in the percentage of (14)C from allantoic acid and allantoin recovered in the first trifoliolate, provided some support for the direct xylem-to-phloem transfer of these compounds, but did not preclude the involvement of indirect transfer. Data on stem retention and foliar distribution, expressed as a function of the relative xylem sap composition, indicated that ureides provide the major sources of nitrogen to all plant parts. There was no consistent distinction in distribution patterns between pairs of similar anionic and neutral compounds. The extent of xylem-to-phloem transfer among the ureido or the amino compounds was inversely related to its prominence in xylem sap.
对处于V(4)生长阶段的固氮大豆（Glycine max）植株正在蒸腾的枝条进行含（14）C标记的含氮化合物的脉冲追踪饲喂（30 - 120分钟），以研究木质部运输的主要溶质的早期去向。通过与[（14）C]菊粉（一种木质部标记物）的叶部分布进行比较，确定尿囊素、尿囊酸、天冬酰胺、谷氨酰胺、天冬氨酸和精氨酸的韧皮部供应分别为木质部液流中输送到发育中的三出复叶的（14）C的约20、10、3、2、5和20倍。在该指示性三出复叶中未代谢的天冬酰胺、天冬氨酸和精氨酸的回收，以及在第一片三出复叶中回收的来自尿囊酸和尿囊素的（14）C百分比的显著下降，为这些化合物从木质部直接向韧皮部转移提供了一些支持，但并不排除间接转移的参与。关于茎部留存和叶部分布的数据，以相对木质部汁液成分的函数表示，表明脲类化合物是所有植物部分氮的主要来源。在成对的相似阴离子和中性化合物之间，分布模式没有一致的区别。脲类或氨基化合物之间木质部向韧皮部的转移程度与其在木质部汁液中的突出程度呈负相关。
