相信所有的事与怀疑所有的事在本质上其实是相同的——(这两种不成熟的做法)都忽视了思考的重要性。~~~~儒勒·昂利·庞加莱,La Science et l'Hypothèse1901?

根瘤与固氮

(A) Soybean roots can interact with rhizobium bacteria and form root nodules. (B) Cross-section shows that, as an organ, the nodule contains cortical cells and vascular bundles outside, as well as parenchyma cells inside that are infected by rhizobia and responsible to the nitrogen fixation. Leghemoglobin is present in these cells and therefore, resulting in a pink color. (C) Transmission electron microscopy shows parenchyma cells can be divided into two kinds of cells: infected cells (INF) and uninfected cells(UN) (from M.L. Guerinot, Dartmouth College). In infected cells, bacteria and their surrounded plant-derived membrane forms symbiosome where nitrogen fixation takes place. One peribacteroid membrane (PBM) is indicated in blue circle, and one bacteroid is indicated in red circle.

豆科植物可以与土壤中的根瘤菌发生信号通讯,并与之建立互惠共生关系。在共生作用建立过程中,豆科植物根部为容纳根瘤菌形成新的次生器官--根瘤(root nodule)。根瘤菌在根瘤中将空气中的氮气固定为供植物吸收的氨;同时,植物为根瘤菌提供生长和固氮所需的营养物质。当根瘤菌沿着侵染线到达根瘤原基后,被释放到根瘤细胞中,这时根瘤菌被一层植物细胞来源的膜所包被,形成类似于细胞器的结构,称为共生体(symbiosome)。共生体是共生固氮的核心部分,它主要由三个部分构成:(1)外面的膜结构,称为共生体膜(symbiosome membrane,SM)或类菌体外周膜(peribacteroid membrane,PBM);(2)被包被的根瘤菌,现在称为类菌体(bacteroid);(3)两者之间的空间,称为类菌体外周腔(peribacteroid space, PBS)。其中,共生体膜是根瘤菌与植物之间进行物质交换和信息交流的媒介,其结构完整性和功能完整性直接影响着固氮效率。因此,共生体膜的发生和功能维系机制是共生固氮研究的关键和热点。我们的研究关注于豆科植物共生固氮过程中根瘤菌是如何进入细胞成为共生体,以及有功能的共生体是如何形成并发挥固氮功能。