Department of Plant Physiology, Faculty of Science, University of Extremadura, Avda de Elvas s/n, 06006 Badajoz, Spain.
J Exp Bot. 2011 Aug;62(13):4447-65. doi: 10.1093/jxb/err124. Epub 2011 Jun 1.
After fruit ripening, many fruit-tree species undergo massive natural fruit abscission. Olive (Olea europaea L.) is a stone-fruit with cultivars such as Picual (PIC) and Arbequina (ARB) which differ in mature fruit abscission potential. Ethylene (ET) is associated with abscission, but its role during mature fruit abscission remains largely uncharacterized. The present study investigates the possible roles of ET and polyamine (PA) during mature fruit abscission by modulating genes involved in the ET signalling and biosynthesis pathways in the abscission zone (AZ) of both cultivars. Five ET-related genes (OeACS2, OeACO2, OeCTR1, OeERS1, and OeEIL2) were isolated in the AZ and adjacent cells (AZ-AC), and their expression in various olive organs and during mature fruit abscission, in relation to interactions between ET and PA and the expression induction of these genes, was determined. OeACS2, OeACO2, and OeEIL2 were found to be the only genes that were up-regulated in association with mature fruit abscission. Using the inhibition of ET and PA biosynthesis, it is demonstrated that OeACS2 and OeEIL2 expression are under the negative control of PA while ET induces their expression in AZ-AC. Furthermore, mature fruit abscission depressed nitric oxide (NO) production present mainly in the epidermal cells and xylem of the AZ. Also, NO production was differentially responsive to ET, PA, and different inhibitors. Taken together, the results indicate that PA-dependent ET signalling and biosynthesis pathways participate, at least partially, during mature fruit abscission, and that endogenous NO and 1-aminocyclopropane-1-carboxylic acid maintain an inverse correlation, suggesting an antagonistic action of NO and ET in abscission signalling.
果实成熟后，许多果树物种会经历大量的自然果实脱落。油橄榄（Olea europaea L.）是一种核果，其品种如皮夸尔（PIC）和阿贝吉纳（ARB）在成熟果实脱落潜力上有所不同。乙烯（ET）与脱落有关，但它在成熟果实脱落过程中的作用在很大程度上仍未得到充分描述。本研究通过调节两个品种的脱落区（AZ）中参与 ET 信号转导和生物合成途径的基因，研究 ET 和多胺（PA）在成熟果实脱落过程中的可能作用。在 AZ 和相邻细胞（AZ-AC）中分离了 5 个 ET 相关基因（OeACS2、OeACO2、OeCTR1、OeERS1 和 OeEIL2），并确定了它们在各种橄榄器官中的表达以及与 ET 和 PA 相互作用以及这些基因表达诱导的成熟果实脱落过程中的表达。发现 OeACS2、OeACO2 和 OeEIL2 是唯一与成熟果实脱落相关的上调基因。通过抑制 ET 和 PA 的生物合成，证明 OeACS2 和 OeEIL2 的表达受 PA 的负调控，而 ET 诱导它们在 AZ-AC 中的表达。此外，成熟果实脱落会抑制主要存在于 AZ 表皮细胞和木质部中的一氧化氮（NO）的产生。此外，NO 的产生对 ET、PA 和不同抑制剂的反应不同。综上所述，结果表明，PA 依赖性 ET 信号转导和生物合成途径至少部分参与了成熟果实脱落，内源性 NO 和 1-氨基环丙烷-1-羧酸（1-aminocyclopropane-1-carboxylic acid，ACC）保持着相反的相关性，表明 NO 和 ET 在脱落信号中存在拮抗作用。
