Pomology Department, Aula Dei Experimental Station-CSIC, Avda Montañana 1005, 50059, Saragossa, Spain.
Arnold Arboretum of Harvard University, 1300 Centre St., Boston, MA, 02131, USA.
Plant Reprod. 2019 Sep;32(3):291-305. doi: 10.1007/s00497-019-00370-z. Epub 2019 May 2.
AGP-rich glycoproteins mediate pollen-ovule interactions and cell patterning in the embryo sac of apple before and after fertilization. Glycoproteins are significant players in the dialog that takes place between growing pollen tubes and the stigma and style in the angiosperms. Yet, information is scarce on their possible involvement in the ovule, a sporophytic organ that hosts the female gametophyte. Apple flowers have a prolonged lapse of time between pollination and fertilization, offering a great system to study the developmental basis of glycoprotein secretion and their putative role during the last stages of the progamic phase and early seed initiation. For this purpose, the sequential pollen tube elongation within the ovary was examined in relation to changes in arabinogalactan proteins (AGPs) in the tissues of the ovule before and after fertilization. To evaluate what of these changes are developmentally regulated, unpollinated and pollinated flowers were compared. AGPs paved the pollen tube pathway in the ovules along the micropylar canal, and the nucellus entrance toward the synergids, which also developmentally accumulated AGPs at the filiform apparatus. Glycoproteins vanished from all these tissues following pollen tube passage, strongly suggesting a role in pollen-ovule interaction. In addition, AGPs marked the primary cell walls of the haploid cells of the female gametophyte, and they further built up in the cell walls of the embryo sac and developing embryo, layering the interactive walls of the three generations hosted in the ovule, the maternal sporophytic tissues, the female gametophyte, and the developing embryo.
富含 AGP 的糖蛋白在苹果胚胎囊受精前后介导花粉-胚珠的相互作用和细胞模式。糖蛋白在花粉管和被子植物柱头花柱之间的对话中扮演着重要的角色。然而，关于它们在胚珠中的可能参与情况的信息却很少，胚珠是一个孢子体器官，容纳着雌性配子体。苹果花在授粉和受精之间有很长的时间间隔，这为研究糖蛋白分泌的发育基础及其在progamic 阶段末期和早期种子起始过程中的潜在作用提供了一个很好的系统。为此，在授粉前后，检查了子房内花粉管的顺序伸长与胚珠组织中阿拉伯半乳聚糖蛋白 (AGP) 的变化之间的关系。为了评估这些变化中有哪些是发育调控的，比较了未授粉和授粉的花朵。AGP 在胚珠中沿着珠孔管和助细胞入口处的花粉管途径铺成，助细胞也在丝状器处发育积累 AGP。授粉后，所有这些组织中的糖蛋白都消失了，强烈表明其在花粉-胚珠相互作用中具有重要作用。此外，AGP 标记了雌性配子体中单倍体细胞的初生细胞壁，并且在胚囊和发育中的胚的细胞壁中进一步积累，在胚珠、母体孢子体组织、雌性配子体和发育中的胚中，为三代组织的相互作用壁分层。
