Camacho-Fernández Carolina, Seguí-Simarro Jose M, Mir Ricardo, Boutilier Kim, Corral-Martínez Patricia
Cell Biology Group, COMAV Institute, Universitat Politècnica de València, Valencia, Spain.
Bioscience, Wageningen University and Research, Wageningen, Netherlands.
Front Plant Sci. 2021 Oct 6;12:737139. doi: 10.3389/fpls.2021.737139. eCollection 2021.
Microspore cultures generate a heterogeneous population of embryogenic structures that can be grouped into highly embryogenic structures [exine-enclosed (EE) and loose bicellular structures (LBS)] and barely embryogenic structures [compact callus (CC) and loose callus (LC) structures]. Little is known about the factors behind these different responses. In this study we performed a comparative analysis of the composition and architecture of the cell walls of each structure by confocal and quantitative electron microscopy. Each structure presented specific cell wall characteristics that defined their developmental fate. EE and LBS structures, which are responsible for most of the viable embryos, showed a specific profile with thin walls rich in arabinogalactan proteins (AGPs), highly and low methyl-esterified pectin and callose, and a callose-rich subintinal layer not necessarily thick, but with a remarkably high callose concentration. The different profiles of EE and LBS walls support the development as suspensorless and suspensor-bearing embryos, respectively. Conversely, less viable embryogenic structures (LC) presented the thickest walls and the lowest values for almost all of the studied cell wall components. These cell wall properties would be the less favorable for cell proliferation and embryo progression. High levels of highly methyl-esterified pectin are necessary for wall flexibility and growth of highly embryogenic structures. AGPs seem to play a role in cell wall stiffness, possibly due to their putative role as calcium capacitors, explaining the positive relationship between embryogenic potential and calcium levels.
小孢子培养产生的胚性结构群体具有异质性，可分为高胚性结构[外壁包被的（EE）和松散的双细胞结构（LBS）]和低胚性结构[致密愈伤组织（CC）和松散愈伤组织（LC）结构]。对于这些不同反应背后的因素知之甚少。在本研究中，我们通过共聚焦显微镜和定量电子显微镜对每种结构的细胞壁组成和结构进行了比较分析。每种结构都呈现出特定的细胞壁特征，这些特征决定了它们的发育命运。EE和LBS结构负责产生大多数有活力的胚，它们呈现出特定的特征，具有富含阿拉伯半乳聚糖蛋白（AGP）、高度和低度甲基酯化果胶以及胼胝质的薄壁，以及富含胼胝质的内膜下层，该层不一定厚，但胼胝质浓度极高。EE和LBS细胞壁的不同特征分别支持了无胚柄胚和有胚柄胚的发育。相反，活力较低的胚性结构（LC）呈现出最厚的壁，并且几乎所有研究的细胞壁成分的值都最低。这些细胞壁特性对细胞增殖和胚发育进程不利。高度甲基酯化的果胶水平高对于高胚性结构的壁柔韧性和生长是必需的。AGP似乎在细胞壁硬度中起作用，这可能是由于它们作为钙载体的假定作用，解释了胚性潜力与钙水平之间的正相关关系。
