Laboratoire des Interactions Plantes-Microbes-Environnement (LIPME), Université de Toulouse, INRA, CNRS, INSA, 31326 Castanet-Tolosan, France.
Faculty of Chemistry, Biotechnology and Food Sciences, Norwegian University of Life Sciences, Ås, Norway.
Biochem Soc Trans. 2021 Feb 26;49(1):495-505. doi: 10.1042/BST20200989.
The interaction between rhizobia and their legume host plants conduces to the formation of specialized root organs called nodules where rhizobia differentiate into bacteroids which fix atmospheric nitrogen to the benefit of the plant. This beneficial symbiosis is of importance in the context of sustainable agriculture as legumes do not require the addition of nitrogen fertilizer to grow. Interestingly, nitric oxide (NO) has been detected at various steps of the rhizobium-legume symbiosis where it has been shown to play multifaceted roles. Both bacterial and plant partners are involved in NO synthesis in nodules. To better understand the role of NO, and in particular the role of bacterial NO, at all steps of rhizobia-legumes interaction, the enzymatic sources of NO have to be elucidated. In this review, we discuss different enzymatic reactions by which rhizobia may potentially produce NO. We argue that there is most probably no NO synthase activity in rhizobia, and that instead the NO2- reductase nirK, which is part of the denitrification pathway, is the main bacterial source of NO. The nitrate assimilation pathway might contribute to NO production but only when denitrification is active. The different approaches to measure NO in rhizobia are also addressed.
根瘤菌与其豆科宿主植物之间的相互作用导致了专门的根器官的形成，这些根器官被称为根瘤，在根瘤中，根瘤菌分化为类菌体，将大气中的氮固定下来，从而使植物受益。这种有益的共生关系在可持续农业中非常重要，因为豆类植物不需要添加氮肥来生长。有趣的是，一氧化氮（NO）已在根瘤菌-豆科植物共生的各个阶段被检测到，并且已经证明它具有多方面的作用。在根瘤中，细菌和植物伙伴都参与了 NO 的合成。为了更好地理解 NO 的作用，特别是细菌 NO 的作用，在根瘤菌-豆科植物相互作用的所有阶段，必须阐明 NO 的酶源。在这篇综述中，我们讨论了根瘤菌可能产生 NO 的不同酶促反应。我们认为，根瘤菌中很可能没有 NO 合酶活性，而是反硝化途径的一部分，即亚硝酸盐还原酶 nirK，是细菌中 NO 的主要来源。硝酸盐同化途径可能有助于 NO 的产生，但只有在反硝化作用活跃时才会如此。还讨论了测量根瘤菌中 NO 的不同方法。
