Iron (Fe), an essential element for plant growth, is abundant in soil but with low bioavailability. Thus, plants developed specialized mechanisms to sequester the element. Beneficial microbes have recently become a favored method to promote plant growth through increased uptake of essential micronutrients, like Fe, yet little is known of their mechanisms of action. Functional mutants of the epiphytic bacterium Azospirillum brasilense, a prolific grass-root colonizer, were used to examine mechanisms for promoting iron uptake in Zea mays. Mutants included HM053, FP10, and ipdC, which have varying capacities for biological nitrogen fixation and production of the plant hormone auxin. Using radioactive iron-59 tracing and inductively coupled plasma mass spectrometry, we documented significant differences in host uptake of Fe^2+/3+ correlating with mutant biological function. Radioactive carbon-11, administered to plants as ¹¹CO₂, provided insights into shifts in host usage of ‘new’ carbon resources in the presence of these beneficial microbes. Of the mutants examined, HM053 exhibited the greatest influence on host Fe uptake with increased plant allocation of ¹¹C-resources to roots where they were transformed and exuded as ¹¹C-acidic substrates to aid in Fe-chelation, and increased C-11 partitioning into citric acid, nicotianamine and histidine to aid in the in situ translocation of Fe once assimilated.

铁（Fe）是植物生长必需的元素，土壤中含量丰富，但生物利用度较低。因此，植物开发出了专门的机制来隔离该元素。有益微生物最近已成为一种受欢迎的方法，通过增加铁等必需微量营养素的吸收来促进植物生长，但对其作用机制知之甚少。附生细菌巴西固氮螺菌（一种多产的草根定植菌）的功能突变体被用来研究促进玉米铁吸收的机制。突变体包括 HM053、FP10 和ipdC ，它们具有不同的生物固氮和植物激素生长素生产能力。使用放射性铁 59 示踪和电感耦合等离子体质谱，我们记录了宿主对 Fe ^2+/3+的吸收与突变生物功能相关的显着差异。放射性碳-11以¹¹ CO ₂的形式施用于植物，为了解在这些有益微生物存在的情况下宿主对“新”碳资源的使用变化提供了见解。在所检查的突变体中，HM053 对宿主 Fe 吸收的影响最大，增加了植物向根部分配¹¹ C 资源，根部进行转化并作为¹¹ C 酸性底物渗出以帮助 Fe 螯合，并增加了 C-11 分配转化为柠檬酸、烟酰胺和组氨酸，以帮助同化后的铁原位易位。