Meeting Agricultural Sustainability through Plant Growth Promoting Bacteria: An Examination of the Mechanisms for Improved Host Uptake of Zinc Nutrient in Maize using Functional Mutants of Azospirillum brasilense

Stacy Wilder; Alexandra Housh; Mary Benoit; Stephanie Scott; Garren Powell; Michael Schueller; Richard Ferrieri

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Meeting Agricultural Sustainability through Plant Growth Promoting Bacteria: An Examination of the Mechanisms for Improved Host Uptake of Zinc Nutrient in Maize using Functional Mutants of Azospirillum brasilense

Stacy Lynn Wilder

^{*

1},

Alexandra Bauer Housh

^{1, 2, 3},

Mary Benoit

^{1, 4},

Stephanie Scott

^{1, 5},

Garren Powell

^{1, 5},

Michael Schueller

^{1, 2},

Richard A. Ferrieri

^{*

1, 2, 3, 4}

¹ Missouri Research Reactor Center, University of Missouri, Columbia, MO 65211 USA
² Chemistry Department, University of Missouri, Columbia, MO 65211 USA
³ Interdisciplinary Plant Group, University of Missouri, Columbia, MO 65211 USA
⁴ Division of Plant Sciences, University of Missouri, Columbia, MO 65211 USA
⁵ Department of Biochemistry, University of Missouri, Columbia, MO 65211

Published: 01 May 2021 by MDPI in The 1st International Electronic Conference on Agronomy session Sustainable Management Practices for Soil Health and Food Security

https://doi.org/10.3390/IECAG2021-09715 (registering DOI)

Abstract:

Zinc (Zn) is an essential micronutrient for plant growth and development. Plants can be lacking in Zn since as a trace element it is subject to widespread soil deficiencies. These deficiencies can arise through a lack of diverse agricultural practices, as well as climatic extremes causing excessive soil weathering. It has been estimated that 30% of global arable lands are deficient in Zn resulting in substantial reduction in yield. In recent agricultural practices, plant growth promoting bacteria (PGPB) are finding increased use for reducing crop losses due to conditions of the soil. Among the PGPB, the genus Azospirillum—with an emphasis on A. brasilense—is probably the most studied microorganism for the mitigation of plant stress. Here we report the investigation of functional mutants HM053, ipdC and FP10 of A. brasilense to understand how the biological functions of these microorganisms can affect host Zn uptake. HM053 is a Nif ⁺ constitutively expressed strain that hyper-fixes N₂ and produces high levels of the plant relevant hormone auxin. FP10 is a Nif^- strain that is deficient in N₂-fixation and produces auxin. ipdC is a strain that is deficient in auxin production but fixes N₂. Zinc uptake was measured in laboratory-based studies of 3-week-old plants using radioactive Zn-65 (t_½ =244 days). Uptake kinetics of the tracer were measured using dedicated radiation detectors. Afterwards, tissues were harvested and counted for levels of Zn-65 radioactivity that had accumulated within the roots and shoots of the plant. Principal Component Analysis using XLSTAT software provided comparisons between microbial biological functions and host Zn-65 accumulation. Results showed that low microbial auxin producing capacity resulted in the greatest accumulation of Zn-65 by the host. This research was supported by Agriculture and Food Research Initiative Award No. 2017-67013-26216 from the USDA National Institute of Food and Agriculture and through a startup award from the University of Missouri administered through University of Missouri Research Reactor Center.