Department of Biotechnology and Systems Biology, National Institute of Biology, Ljubljana, Slovenia.
Jožef Stefan International Postgraduate School, Ljubljana, Slovenia.
Plant Biol (Stuttg). 2018 Jul;20(4):722-728. doi: 10.1111/plb.12730. Epub 2018 Apr 26.
The abscission of tomato leaves occurs in the petiole abscission zone, and its late stage includes two spatially divided processes: cell separation and programmed cell death (PCD). Both of these processes are regulated by ethylene. The last step in ethylene biosynthesis is conversion of 1-aminocyclopropane-1-carboxylic acid to ethylene, which is catalysed by the enzyme 1-aminocyclopropane-1-carboxylate oxidase (ACO); however, the location of ACO in the leaf petiole abscission zone is not known. The tomato gene LeLX encodes ribonuclease LX, which is a marker for PCD and is induced by ethylene during abscission, but its association with ACO has not been explored. In a tomato transgenic line 1-7 with inhibited expression of LeLX showing delayed leaf abscission, the morphology and ultrastructure of the leaf petiole abscission zone was examined. In this zone of the cv.'VF36' and of a transgenic line 1-7, spatiotemporal differences in expression of LeACO1 and LeACO4 were analysed and ACO protein was detected immunohistochemically. In comparison to wild-type plants, there were no obvious morphological and ultrastructural features in the abscission zone of plants of a transgenic line 1-7 before and after abscission induction. LeACO1 expression was low before abscission induction, and increased 24 h after induction, although with no apparent spatial pattern. In contrast, LeACO4 was expressed before abscission induction, and its transcript level declined 24 h after induction on the distal side of the abscission zone fracture. In the LeLX-inhibited transgenic line, there were no significant differences in LeACO1 and LeACO4 expression in the petiole abscission zone, in comparison to wild-type plants. In addition, the ACO protein was immunolocalised to the vascular tissues that traverse the petiole abscission zone in plants of wild type and of a transgenic line 1-7; and additionally in the plane of future abscission zone fracture of transgenic-line plants. The results suggest temporal differential expression of the LeACO genes in tomato leaf petioles and vascular localisation of ACO1 protein. Additionally, the results indicate that expression of LeACO genes is not affected by suppression of the LeLX expression.
番茄叶片的脱落发生在叶柄脱落区，其晚期包括两个空间上分开的过程：细胞分离和细胞程序性死亡（PCD）。这两个过程都受乙烯的调节。乙烯生物合成的最后一步是将 1-氨基环丙烷-1-羧酸转化为乙烯，这一过程由酶 1-氨基环丙烷-1-羧酸氧化酶（ACO）催化；然而，ACO 在叶片叶柄脱落区的位置尚不清楚。番茄基因 LeLX 编码核糖核酸酶 LX，它是 PCD 的标志物，并且在脱落过程中受乙烯诱导，但它与 ACO 的关系尚未被探索。在一个表达 LeLX 受抑制的番茄转基因系 1-7 中，观察到叶片脱落延迟，叶片叶柄脱落区的形态和超微结构。在 cv.‘VF36’和转基因系 1-7 的这个区域，分析了 LeACO1 和 LeACO4 的时空差异表达，并通过免疫组织化学检测了 ACO 蛋白。与野生型植物相比，在转基因系 1-7 的叶柄脱落区，在诱导脱落前后没有明显的形态和超微结构特征。LeACO1 的表达在诱导脱落前较低，诱导后 24 小时增加，尽管没有明显的空间模式。相比之下，LeACO4 在诱导脱落前表达，其转录水平在诱导后 24 小时在脱落区断裂的远端下降。在 LeLX 抑制的转基因系中，与野生型植物相比，叶柄脱落区的 LeACO1 和 LeACO4 表达没有显著差异。此外，在野生型和转基因系 1-7 的植物中，ACO 蛋白被免疫定位到穿过叶柄脱落区的维管束组织；此外，在转基因系植物未来脱落区断裂的平面上也有免疫定位。结果表明，番茄叶片叶柄中 LeACO 基因的表达具有时间差异，并且 ACO1 蛋白在维管束组织中定位。此外，结果表明，LeACO 基因的表达不受 LeLX 表达抑制的影响。
