Department of Botany, University of Innsbruck , Sternwartestraße 15, 6020 Innsbruck, Austria.
Philos Trans R Soc Lond B Biol Sci. 2024 Nov 18;379(1914):20230356. doi: 10.1098/rstb.2023.0356. Epub 2024 Sep 30.
Recent research on a special type of sexual reproduction and zygospore formation in Zygnematophyceae, the sister group of land plants, is summarized. Within this group, gamete fusion occurs by conjugation. Zygospore development in and is highlighted, which has recently been studied using Raman spectroscopy, allowing chemical imaging and detection of changes in starch and lipid accumulation. Three-dimensional reconstructions after serial block-face scanning electron microscopy (SBF-SEM) or focused ion beam SEM (FIB-SEM) made it possible to visualize and quantify cell wall and organelle changes during zygospore development. The zygospore walls undergo strong modifications starting from uniform thin cell walls to a multilayered structure. The mature cell wall is composed of a cellulosic endospore and exospore and a central mesospore built up by aromatic compounds. In , the exospore and endospore consist of thick layers of helicoidally arranged cellulose fibrils, which are otherwise only known from stone cells of land plants. While starch is degraded during maturation, providing building blocks for cell wall formation, lipid droplets accumulate and fill large parts of the ripe zygospores, similar to spores and seeds of land plants. Overall, data show similarities between streptophyte algae and embryophytes, suggesting that the genetic toolkit for many land plant traits already existed in their shared algal ancestor. This article is part of the theme issue 'The evolution of plant metabolism'.
本文总结了关于接合藻纲（与陆地植物的姐妹群）中一种特殊有性生殖和接合孢子形成的最新研究。在该类群中，配子融合通过接合发生。重点介绍了 和 的接合孢子发育，最近使用拉曼光谱对其进行了研究，允许对淀粉和脂质积累的变化进行化学成像和检测。通过连续块面扫描电子显微镜（SBF-SEM）或聚焦离子束扫描电子显微镜（FIB-SEM）的三维重建，使得在接合孢子发育过程中可视化和量化细胞壁和细胞器的变化成为可能。从均匀的薄细胞壁到多层结构，接合孢子壁发生强烈的变化。成熟的细胞壁由纤维素内孢子和外孢子以及由芳香族化合物构成的中央中孢子组成。在 中，外孢子和内孢子由螺旋排列的纤维素纤维厚层组成，否则这些纤维素纤维仅见于陆地植物的石细胞中。在成熟过程中，淀粉被降解，为细胞壁形成提供构建块，而脂质滴则积累并填充成熟接合孢子的大部分，类似于陆地植物的孢子和种子。总的来说，数据显示了绿藻和胚胎植物之间的相似性，表明许多陆地植物特征的遗传工具包已经存在于它们共同的藻类祖先中。本文是主题为“植物代谢的进化”的特刊的一部分。
