Department of Botany, University of Western Australia, Nedlands, Western Australia 6009.
Plant Physiol. 1979 Jun;63(6):1076-81. doi: 10.1104/pp.63.6.1076.
Amino compounds representative of the major N solutes of xylem sap were pulse-fed (10 to 20 minutes) singly in (14)C-labeled form to cut transpiring shoots of white lupin (Lupinus albus L.). (14)C distribution was studied by autoradiography and radioassays of phloem sap, leaflet tissues, and shoot parts harvested at intervals after labeling. Primary distribution of N by xylem was simulated using a 20-minute labeling pulse followed by a 30-minute chase in unlabeled xylem sap. Shoots fed (14)C-labeled asparagine, glutamine, valine, serine, or arginine showed intense labeling of leaflet veins and marked retention (35 to 78%) of (14)C by stem + petioles. Shoots fed (14)C-labeled aspartic acid or glutamic acid showed heaviest (14)C accumulation in interveinal regions of leaflets and low uptake (11 to 20%) of (14)C by stem + petioles. Departing leaf traces were major sites of uptake of all amino compounds, and the implications of this were evaluated. Fruits acquired only 1 to 5% of the fed label directly from xylem, but more than doubled their intake during the period 30 to 160 minutes after feeding through receipt of (14)C transferred from xylem to phloem in stem and leaves. (14)C-Labeled asparagine and valine transferred directly from xylem to phloem, but the (14)C of (14)C-labeled aspartic acid and arginine appeared in phloem mainly as metabolic products of the fed compound. The labeling of the soluble pool of leaflets reflected these differences. The significance of heterogeneity in distribution and metabolism of xylem amino compounds in the shoot was discussed.
用 14C 标记的氨基酸代表木质部汁液中的主要 N 溶质，对正在蒸腾的白羽扇豆（ Lupinus albus L.）切枝进行脉冲（10-20 分钟）单一喂养。通过放射性自显影和对标记后不同时间收获的韧皮汁液、小叶组织和枝条部分进行放射性测定，研究了 14C 的分布。用 20 分钟的标记脉冲后进行 30 分钟的无标记木质部汁液追踪，模拟了 N 通过木质部的初步分配。用 14C 标记的天冬酰胺、谷氨酰胺、缬氨酸、丝氨酸或精氨酸喂养的枝条，叶片叶脉强烈标记，并保留（35-78%）14C 在茎+叶柄中。用 14C 标记的天冬氨酸或谷氨酸喂养的枝条，在叶片的脉间区域积累了最多的 14C，而茎+叶柄中 14C 的摄取量较低（11-20%）。离开的叶迹是所有氨基酸化合物吸收的主要部位，并对其进行了评估。果实仅从木质部直接获得 1-5%的喂养标签，但在喂食后 30-160 分钟期间，通过从木质部到茎和叶中的韧皮部转移的 14C 吸收，使摄入量增加了一倍以上。14C 标记的天冬酰胺和缬氨酸直接从木质部转移到韧皮部，但 14C 标记的天冬氨酸和精氨酸的 14C 主要作为所喂养化合物的代谢产物出现在韧皮部中。小叶可溶性池的标记反映了这些差异。讨论了枝条中木质部氨基酸化合物分布和代谢异质性的意义。
