Ishiwatari Y, Honda C, Kawashima I, Nakamura S, Hirano H, Mori S, Fujiwara T, Hayashi H, Chino M
Department of Applied Biological Chemistry, University of Tokyo, Japan.
Planta. 1995;195(3):456-63. doi: 10.1007/BF00202605.
Sieve tubes play important roles in the transfer of nutrients as well as signals. Hundreds of proteins were found in pure phloem sap collected from rice (Oryza sativa L. cv. Kantou) plants through the cut ends of insect stylets. These proteins may be involved in nutrient transfer and signal transduction. To characterize the nature of these proteins, the partial amino-acid sequence of a 13-kDa protein, named RPP13-1, that was abundant in the pure phleom sap was determined. A cDNA clone of 687 bp, containing an open reading frame of 122 amino acids, was isolated using corresponding oligonucleotides as a probe. The deduced amino-acid sequence was very similar to that of the ubiquitous thiol redox protein, thioredoxin. The consensus sequences of thioredoxins are highly conserved. No putative signal peptide was identified. Antiserum against wheat thioredoxin h cross-reacted with RPP13-1 in the phloem sap of rice plants. RPP13-1 produced in Escherichia coli was reactive to antiserum against wheat thioredoxin h. Both E. coli-produced RPP13-1 and the phloem sap proteins catalyzed the reduction of the disulfide bonds of insulin in the presence of dithiothreitol. These results indicate that an active thioredoxin is a major protein translocating in rice sieve tubes.
筛管在营养物质以及信号的传递中发挥着重要作用。通过昆虫口针的切口从水稻（Oryza sativa L. cv. Kantou）植株收集的纯韧皮部汁液中发现了数百种蛋白质。这些蛋白质可能参与营养物质的转运和信号转导。为了表征这些蛋白质的性质，测定了在纯韧皮部汁液中含量丰富的一种13 kDa蛋白质（命名为RPP13 - 1）的部分氨基酸序列。使用相应的寡核苷酸作为探针，分离出一个687 bp的cDNA克隆，其包含一个122个氨基酸的开放阅读框。推导的氨基酸序列与普遍存在的硫醇氧化还原蛋白硫氧还蛋白非常相似。硫氧还蛋白的共有序列高度保守。未鉴定出推定的信号肽。抗小麦硫氧还蛋白h的抗血清与水稻植株韧皮部汁液中的RPP13 - 1发生交叉反应。在大肠杆菌中产生的RPP13 - 1与抗小麦硫氧还蛋白h的抗血清发生反应。在二硫苏糖醇存在的情况下，大肠杆菌产生的RPP13 - 1和韧皮部汁液蛋白都催化胰岛素二硫键的还原。这些结果表明，一种活性硫氧还蛋白是在水稻筛管中转运的主要蛋白质。
