Abstract—NO is a gaseous signaling redox-active molecule that functions in various eukaryotes. However, its synthesis, turnover, and effects in cells are specific in plants in several aspects. Compared with higher plants, the role of NO in Chlorophyta has not been investigated enough. However, some of the mechanisms for controlling the levels of this signaling molecule have been characterized in model green algae. In Chlamydomonas reinhardtii, NO synthesis is carried out by a dual system of nitrate reductase and NO-forming nitrite reductase. Other mechanisms that might produce NO from nitrite are associated with components of the mitochondrial electron-transport chain. In addition, NO formation in some green algae proceeds by an oxidative mechanism similar to that in mammals. The recent discovery of L-arginine-dependent NO synthesis in the colorless alga Polytomella parva suggests the existence of a protein complex with enzyme activities that are similar to animal nitric oxide synthase. This latter finding paves the way for further research into potential members of the NO synthases family in Chlorophyta. Beyond synthesis, the regulatory processes to maintain intracellular NO levels are also an integral part for its function in cells. Members of the truncated hemoglobins family with dioxygenase activity can convert NO to nitrate, as was shown for C. reinhardtii. In addition, the implication of NO reductases in NO scavenging has also been described. Even more intriguing, unlike in animals, the typical NO/cGMP signaling module appears not to be used by green algae. S-nitrosylated glutathione, which is considered the main reservoir for NO, provides NO signals to proteins. In Chlorophyta, protein S-nitrosation is one of the key mechanisms of action of the redox molecule. In this review, we discuss the current state-of-the-art and possible future directions related to the biology of NO in green algae.

摘要：NO 是一种气体信号氧化还原活性分子，在多种真核生物中发挥作用。然而，它的合成、周转和在细胞中的作用在几个方面是植物所特有的。与高等植物相比，NO在绿藻中的作用尚未得到足够的研究。然而，控制这种信号分子水平的一些机制已经在绿藻模型中得到了表征。在莱茵衣藻中，NO合成是通过硝酸还原酶和形成NO的亚硝酸还原酶的双重系统进行的。其他可能从亚硝酸盐产生 NO 的机制与线粒体电子传递链的组成部分有关。此外，一些绿藻中一氧化氮的形成是通过类似于哺乳动物的氧化机制进行的。最近在无色藻类Polytomella parva中发现L-精氨酸依赖性NO 合成表明存在一种具有与动物一氧化氮合酶类似的酶活性的蛋白质复合物。后一项发现为进一步研究绿藻中 NO 合酶家族的潜在成员铺平了道路。除了合成之外，维持细胞内 NO 水平的调节过程也是其在细胞中发挥功能的一个组成部分。具有双加氧酶活性的截短血红蛋白家族的成员可以将 NO 转化为硝酸盐，如莱茵衣藻所示。此外，还描述了NO还原酶在NO清除中的作用。更有趣的是，与动物不同，绿藻似乎不使用典型的 NO/cGMP 信号模块。S-亚硝基化谷胱甘肽被认为是 NO 的主要储存库，向蛋白质提供 NO 信号。在绿藻中，蛋白质 S-亚硝化是氧化还原分子的关键作用机制之一。在这篇综述中，我们讨论了与绿藻中 NO 生物学相关的当前最新技术和未来可能的方向。