Persistent high-density cultivation farming has led to depletion of essential microelements in soil which can result in decreased crop nutrition. Low nutrient crops contribute to severe, often fatal, micronutrient deficiencies in global populations. This work involves radioanalytical laboratory studies on maize inoculated with Azospirillum brasilense, a prolific grass root colonizing bacteria, to investigate bacterial influence on maize iron assimilation and allocation. Dynamic and quantitative maize 59Fe (t1/2 = 44.5 d) acquisition and root-to-shoot allocation studies with gamma detection reveal bacteria significantly promote whole-plant iron uptake and root-to-shoot allocation relative to non-inoculated controls. Studies with ICP-MS analysis of digested total plant tissues revealed bacteria inoculated plants had 3.8x more 56Fe than non-inoculated controls, while spatial analysis using LA-ICP-MS of root and leaf sections revealed bacteria associated maize had 5.8x more iron in leaf tissue and significantly more iron in the root endodermis compared to control maize. Radio-HPLC and gamma detection were used in combination with radioactive 11C (t1/2 = 20.4 m) to investigate possible mechanisms underlying promotion of iron allocation in maize. 11CO2 was administered to maize leaves and changes in partitioning of ‘new’ carbon into mobile substrate pools were quantified. Metabolism of key iron transport molecules like histidine, citric acid, and nicotianamine were significantly elevated in the presence of the bacteria. Nicotianamine is a precursor to root-excreted iron-chelating phytosiderophores. An increase in phytosiderophore production due to available nicotianamine would account for elevated maize iron uptake.

Leveraging radioanalytical and mass-spectrometry based technologies to investigate iron assimilation and allocation in rhizobacteria-associated maize

2019 Fall National Meeting

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