Phytohormones are pivotal signaling compounds in higher plants, in which they exert their roles intracellularly, but are also released for cell‐to‐cell communication. In unicellular organisms, extracellularly released phytohormones can be involved in chemical crosstalk with other organisms. However, compared to higher plants, hardly any knowledge is available on the roles of phytohormones in green algae. Here, we studied phytohormone composition and extracellular release in aero‐terrestrial Trebouxiophyceae. We investigated (a) which phytohormones are produced and if they are released extracellularly, and if extracellular phytohormone levels are (b) affected by environmental stimuli, and (c) differ between lichen‐forming and non‐lichen‐forming species. Three free‐living microalgae (Apatococcus lobatus, Chloroidium ellipsoideum, and Myrmecia bisecta) and three lichen‐forming microalgae (Asterochloris glomerata, Trebouxia decolorans, and Trebouxia sp.) were studied. Algae were grown on solid media and the following cellular phytohormones were identified by ultra‐high‐performance liquid chromatography coupled with tandem mass spectrometry (UHPLC‐MS/MS): indole‐3‐acetic acid (IAA), indole‐3‐butyric acid (IBA), abscisic acid (ABA), gibberellin A₄ (GA₄), and zeatin (ZT). Furthermore, IAA, IBA, ABA, jasmonic acid (JA), gibberellin A₃ (GA₃), and GA₄ were found to be released extracellularly. IAA and ABA were released by all six species, and IAA was the most concentrated. Phytohormone release was affected by light and water availability, especially IAA in A. glomerata, Trebouxia sp., and C. ellipsoideum. No clear patterns were observed between lichen‐forming and non‐lichen‐forming species. The results are envisaged to contribute valuable baseline information for further studies into the roles of phytohormones in microalgae.

中文翻译：

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陆生微藻（Trebouxiophyceae、Chlorophyta）中植物激素的丰度和细胞外释放作为潜在的化学信号源1。

植物激素是高等植物中的关键信号化合物，它们在细胞内发挥作用，但也被释放用于细胞间通讯。在单细胞生物中，细胞外释放的植物激素可能参与与其他生物的化学串扰。然而，与高等植物相比，关于植物激素在绿藻中的作用几乎没有任何知识。在这里，我们研究了气陆三环藻纲的植物激素组成和细胞外释放。我们研究了（a）产生了哪些植物激素以及它们是否释放到细胞外，以及细胞外植物激素水平是否（b）受到环境刺激的影响，以及（c）地衣形成和非地衣形成物种之间的差异。研究了三种独立生活的微藻（Apatococcus lobatus、Chloroidium ellipsoideum和Myrmecia bisecta）和三种地衣形成微藻（Asterocholis glomerata、Trebouxia decolorans和Trebouxia sp.）。藻类在固体培养基上生长，并通过超高效液相色谱结合串联质谱法 (UHPLC-MS/MS) 鉴定了以下细胞植物激素：吲哚-3-乙酸 (IAA)、吲哚-3-丁酸(IBA)、脱落酸(ABA)、赤霉素A ₄ (GA ₄ )和玉米素(ZT)。此外，发现IAA、IBA、ABA、茉莉酸(JA)、赤霉素A ₃ (GA ₃ )和GA ₄被释放到细胞外。六个物种均释放 IAA 和 ABA，其中 IAA 浓度最高。植物激素的释放受到光照和水分的影响，尤其是A. glomerata、Trebouxia sp. 和C. ellipsoideum中的 IAA 。在地衣形成和非地衣形成物种之间没有观察到明显的模式。研究结果预计将为进一步研究植物激素在微藻中的作用提供有价值的基线信息。