Fisher D B
Department of Biochemistry and Biophysics, Iowa State University, Ames, Iowa.
Plant Physiol. 1970 Feb;45(2):114-8. doi: 10.1104/pp.45.2.114.
The kinetics of (14)C-assimilates in the soybean leaf were studied in pulse labeling and steady state labeling experiments. (14)C-Sucrose apparently served as the ultimate source, at least, of translocated (14)C-sucrose. However, since the specific activity of leaf sucrose reached a maximum within 5 minutes after pulse labeling, whereas that of exported sucrose did not reach a maximum until at least 20 minutes, it appeared that there were two sucrose compartments in the leaf. A possible physical basis for the two compartments may be the mesophyll (a photosynthetic compartment) and a specialized "paraveinal mesophyll" (a nonphotosynthetic compartment), through which photosynthate must pass on its way to the veins.The (14)C kinetics of sterol glucoside, and probably esterified sterol glucoside, were similar to those for (14)C-sucrose export. Sterol glucoside was labeled only in its glucose moiety and was the only stem lipid which became strongly labeled during (14)C-sucrose translocation. These sterol derivatives may act as membrane carriers of sucrose between the translocation stream and surrounding cells.The kinetics of (14)C-sucrose and its movement to the veins are discussed with reference to compartmentation within the leaf and metabolic exchange with other compounds, particularly with starch. Although a simple compartmental model gave a fairly accurate description of (14)C-sucrose kinetics, an entirely accurate model could not be provided, primarily because of loss of (14)C from sucrose, at an unknown rate, to starch.
在脉冲标记和稳态标记实验中研究了大豆叶片中（14）C同化物的动力学。（14）C-蔗糖显然至少是转运的（14）C-蔗糖的最终来源。然而，由于脉冲标记后5分钟内叶片蔗糖的比活性达到最大值，而输出蔗糖的比活性直到至少20分钟才达到最大值，因此叶片中似乎存在两个蔗糖区室。这两个区室可能的物理基础可能是叶肉（一个光合区室）和一个特殊的“脉间叶肉”（一个非光合区室），光合产物必须通过这个区室才能到达叶脉。甾醇糖苷以及可能的酯化甾醇糖苷的（14）C动力学与（14）C-蔗糖输出的动力学相似。甾醇糖苷仅在其葡萄糖部分被标记，并且是在（14）C-蔗糖转运过程中唯一被强烈标记的茎脂类。这些甾醇衍生物可能作为蔗糖在转运流和周围细胞之间的膜载体。参照叶片内的区室化以及与其他化合物，特别是与淀粉的代谢交换，讨论了（14）C-蔗糖的动力学及其向叶脉的移动。尽管一个简单的区室模型对（14）C-蔗糖动力学给出了相当准确的描述，但主要由于蔗糖以未知速率向淀粉损失（14）C，所以无法提供一个完全准确的模型。
