ABSTRACT The year 2020 marks the 150th anniversary of the elucidation of the process of plant organ growth at the cellular level by Julius Sachs (1870). In this Addendum to a Review Article in Molecular Plant, we describe this fundamental discovery and argue that the etiolated grass coleoptile still represents the system of choice for the experimental analysis of auxin (indole-3-acetic acid, IAA)-action. With reference to the phenomenon of ‘tissue tension’, we discuss the acid-growth hypotheses of IAA-induced wall loosening and the process of vacuolar expansion, respectively. IAA-mediated elongation appears to be independent of wall acidification, and may be regulated via the secretion of glycoproteins into the outer epidermal wall, whereby turgor (and tissue) pressure provides the ‘driving force’ for growth. As predicted by the “acid growth-hypothesis”, the fungal phytotoxin Fusicoccin (Fc) induces organ elongation via the rapid secretion of protons. We conclude that “cell elongation” can only be understood at the level of the entire organ that displays biomechanical features not established by single cells. This systems-level approach can be traced back to the work of Sachs (1870).

中文翻译：

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生长素在开发玉米胚芽鞘中的作用：挑战和悬而未决的问题

摘要 2020 年是 Julius Sachs (1870) 从细胞水平阐明植物器官生长过程 150 周年。在这篇 Molecular Plant 综述文章的附录中，我们描述了这一基本发现，并认为黄化的草胚芽鞘仍然是生长素（吲哚-3-乙酸，IAA）作用实验分析的首选系统。参考“组织张力”现象，我们分别讨论了 IAA 引起的壁松动和液泡扩张过程的酸生长假说。IAA 介导的伸长似乎与壁酸化无关，并且可能通过将糖蛋白分泌到外表皮壁来调节，从而膨胀（和组织）压力为生长提供“驱动力”。正如“酸性生长假说”所预测的那样，真菌植物毒素 Fusicoccin (Fc) 通过质子的快速分泌诱导器官伸长。我们得出的结论是，“细胞伸​​长”只能在整个器官的水平上理解，该器官显示出单细胞无法建立的生物力学特征。这种系统级方法可以追溯到 Sachs (1870) 的工作。