Department of Botany, University of Western Australia, Nedlands, Western Australia 6009.
Plant Physiol. 1978 Oct;62(4):495-8. doi: 10.1104/pp.62.4.495.
The ureides, allantoin and allantoic acid, represented major fractions of the soluble nitrogen pool of nodulated plants of cowpea (Vigna unguiculata [L.] Walp. cv. Caloona) throughout vegetative and reproductive growth. Stem and petioles were the principal sites of ureide accumulation, especially in early fruiting.Labeling studies using (14)CO(2) and (15)N(2) and incubation periods of 25 to 245 minutes indicated that synthesis of allantoin and allantoic acid in root nodules involved currently delivered photosynthate and recently fixed N, and that the ureides were exported from nodule to shoot via the xylem. From 60 to 80% of xylem-borne N consisted of ureides; the remainder was glutamine, asparagine, and amino acids. Allantoin predominated in the soluble N fraction of nodules and fruits, allantoin and allantoic acid were present in approximately equal proportions in xylem exudate, stems, and petioles.Extracts of the plant tissue fraction of nitrogen-fixing cowpea nodules contained glutamate synthase (EC 2.6.1.53) and glutamine synthetase (EC 6.3.1.2), but little activity of glutamate dehydrogenase (EC 1.4.1.3). High levels of uricase (EC 1.7.3.3) and allantoinase (EC 3.5.2.5) were also detected. Allantoinase but little uricase was found in extracts of leaflets, pods, and seeds.Balance sheets were constructed for production, storage, and utilization of ureide N during growth. Virtually all (average 92%) of the ureides exported from roots was metabolized on entering the shoot, the compounds being presumably used as N sources for protein synthesis.
在营养生长和生殖生长过程中，豆类植物（豇豆，Vigna unguiculata [L.] Walp. cv. Caloona）根瘤中的尿囊素、尿囊酸和尿素代表了可溶性氮库的主要部分。茎和叶柄是脲积累的主要部位，尤其是在早期结果时。使用 (14)CO(2) 和 (15)N(2) 的标记研究和 25 到 245 分钟的孵育期表明，根瘤中尿囊素和尿囊酸的合成涉及当前提供的光合产物和最近固定的 N，并且这些尿素通过木质部从根瘤中输出到地上部分。在木质部携带的 N 中，有 60-80%是尿素；其余部分是谷氨酰胺、天冬酰胺和氨基酸。在根瘤和果实的可溶性氮部分中，尿囊素占主导地位，而在木质部渗出物、茎和叶柄中，尿囊素和尿囊酸的比例大致相同。固氮豇豆根瘤植物组织部分的提取物含有谷氨酸合酶（EC 2.6.1.53）和谷氨酰胺合酶（EC 6.3.1.2），但谷氨酸脱氢酶（EC 1.4.1.3）的活性很低。还检测到高水平的尿酸酶（EC 1.7.3.3）和尿囊素酶（EC 3.5.2.5）。在叶片、豆荚和种子的提取物中发现了大量的尿囊素酶，但尿酸酶含量很少。在生长过程中，构建了尿素氮的产生、储存和利用的平衡表。从根部输出的尿素几乎全部（平均 92%）在进入地上部分时被代谢，这些化合物可能被用作蛋白质合成的氮源。
