Losada Juan M, Herrero Maria
Arnold Arboretum of Harvard University, 1300 Centre St, Boston, MA 02131, USA.
Department of Organismic and Evolutionary Biology, Harvard University, 16 Divinity Ave, Cambridge, MA 02138, USA.
Ann Bot. 2017 Apr 1;119(6):989-1000. doi: 10.1093/aob/mcw276.
Within the ovary, the obturator bridges the pathway of the pollen tube from the style to the ovule. Despite its widespread presence among flowering plants, its function has only been studied in a handful of species, and the molecules involved in pollen tube-obturator cross-talk have not been explored hitherto. This work evaluates the involvement of glucans and glycoproteins on pollen tube growth in the obturator of apple flowers ( Malus × domestica) .
Pollen tube kinetics were sequentially examined in the pistil and related to changes occurring on the obturator using histochemistry and inmunocytochemistry. To discriminate between changes in the obturator induced by pollen tubes from those developmentally regulated, both pollinated and unpollinated pistils were examined.
Pollen tube growth rates were slow in the stigma, faster in the style and slow again in the ovary. The arrival of pollen tubes at the obturator was concomitant with the secretion of proteins, saccharides and glycoprotein epitopes belonging to extensins and arabinogalactan proteins (AGPs). While some of these secretions - extensins and AGPs labelled by JIM13 - were developmentally regulated, others - AGPs labelled by JIM8 - were elicited by the presence of pollen tubes. Following pollen tube passage, all these glycoproteins were depleted.
The results show a timely secretion of glycoproteins on the obturator surface concomitant with pollen tube arrival at this structure. The fact that their secretion is depleted following pollen tube passage strongly suggests their role in regulating pollen tube access to the ovule. Remarkably, both the regulation of the secretion of the different glycoproteins, as well as their association with the performance of pollen tubes exhibit similarities with those observed in the stigma, in line with their common developmental origin.
在子房内，珠孔道连接着花粉管从花柱到胚珠的路径。尽管其在开花植物中广泛存在，但其功能仅在少数物种中得到研究，迄今为止，尚未探索参与花粉管与珠孔道相互作用的分子。本研究评估了葡聚糖和糖蛋白在苹果花（苹果属× domestica）珠孔道中对花粉管生长的影响。
利用组织化学和免疫细胞化学方法，依次检测雌蕊中花粉管的动力学，并将其与珠孔道上发生的变化相关联。为了区分花粉管诱导的珠孔道变化与发育调控的变化，对授粉和未授粉的雌蕊均进行了检测。
花粉管在柱头处生长速率较慢，在花柱中较快，而在子房中又变慢。花粉管到达珠孔道时，伴随着属于伸展蛋白和阿拉伯半乳聚糖蛋白（AGPs）的蛋白质、糖类和糖蛋白表位的分泌。虽然其中一些分泌物——被JIM13标记的伸展蛋白和AGPs——是受发育调控的，但其他分泌物——被JIM8标记的AGPs——是由花粉管的存在引发的。花粉管通过后，所有这些糖蛋白都被耗尽。
结果表明，珠孔道表面糖蛋白的分泌与花粉管到达该结构同步发生。花粉管通过后其分泌被耗尽这一事实强烈表明它们在调节花粉管进入胚珠方面的作用。值得注意的是，不同糖蛋白分泌的调节及其与花粉管性能的关联与在柱头中观察到的情况相似，这与其共同的发育起源一致。
