DPT CEPIA, INRA, 44316, Nantes, France.
Synchrotron SOLEIL, 91190, Gif-sur-Yvette, France.
Protoplasma. 2019 Jul;256(4):1025-1035. doi: 10.1007/s00709-019-01360-8. Epub 2019 Mar 5.
Sulfur (S) and phosphorus (P) are essential elements for plant growth and physiological functioning. Their deficiency can limit N fixation and nodule development in nodulated legumes. The location of S within nodule tissues could provide insights into S metabolism and its little-known relationship with N fixation. Determinate and indeterminate nodules were inoculated with specific rhizobia and grown hydroaeroponically under sufficient versus deficient P supplies. Cryogenic and freeze-dried thin sections of nodules at the flowering stage were mapped using synchrotron micro-X-ray fluorescence to determine the S distribution within the nodule tissues with a spatial resolution of 2 or 3 μm. A large accumulation of S was found in the middle cortex for both types of nodules. S was also found in all of the other tissues but with a significantly lower signal. In the middle cortex, P deficiency decreased the S maximum fluorescence intensity by 20% and 25% for the determinate and indeterminate nodules, respectively. In addition, Mg and Cl maps were also collected showing that Mg was mostly localized in the middle and inner cortex, forming a Mg-rich ring consisting of several cell layers for the determinate nodules compared with only one cell layer for the indeterminate nodules. Cl was mainly accumulated in the outer cortex. It is concluded that the accumulation of S in the middle cortex is consistent with its involvement in the ionic equilibrium of the nodule, and in the osmotic variation of the inner cortex cell-size, which would regulate nodule permeability to oxygen.
硫（S）和磷（P）是植物生长和生理功能所必需的元素。它们的缺乏会限制共生固氮豆科植物的氮固定和根瘤发育。根瘤组织中 S 的位置可以深入了解 S 代谢及其与氮固定的鲜为人知的关系。将有性和无性结瘤接种特定根瘤菌，并在充足和缺乏 P 供应的条件下进行水培生长。在开花期，使用同步加速器微 X 射线荧光对冷冻和冻干的根瘤薄切片进行映射，以确定根瘤组织内 S 的分布，空间分辨率为 2 或 3 μm。两种类型的根瘤都在中间皮层中发现了大量的 S 积累。在所有其他组织中也发现了 S，但信号明显较低。在中间皮层中，P 缺乏分别使有性和无性根瘤的 S 最大荧光强度降低了 20%和 25%。此外，还收集了 Mg 和 Cl 图谱，表明 Mg 主要定位于中间和内皮层，形成一个由几个细胞层组成的富含 Mg 的环，与无性根瘤只有一个细胞层相比。Cl 主要积累在外皮层。因此，可以得出结论，S 在中间皮层中的积累与其参与根瘤的离子平衡以及内皮层细胞大小的渗透变化有关，这将调节根瘤对氧气的通透性。
