Document Type

Thesis - Open Access

Award Date

2016

Degree Name

Master of Science (MS)

Department / School

Biology and Microbiology

First Advisor

R. Neil Reese

Keywords

endophyte, legume, nitrogen fixation, pediomelum, plant-microbe interactions, root nodule symbiosis

Abstract

Pediomelum esculentum (commonly prairie turnip) is a perennial legume of the Great Plains, consisting of a deep taproot and large edible tuber, and has served as a nutritious staple in Native American diets. The tuber is capable of storing up to 20 percent protein by weight. P. esculentum is a legume, but not a prominent nodule former; instead, it grows in nitrogen-limited soils and produces large amounts of protein. This suggests the involvement of biological nitrogen fixation. We have investigated the presence of diazotrophic endophytes in P. esculentum. Bacteria were isolated from wild plants on nitrogen free media, identified with their partial 16S rRNA gene sequences, and screened for the presence of the nitrogen fixation gene nifH. Select isolates were applied as a coinoculum to seedlings grown under gnotobiotic conditions in a growth chamber with no nitrogen source. Seedlings in both the inoculated and uninoculated group developed nodules and showed no signs of nitrogen stress. Bacteria isolated from the nodules and tubers of both groups were closely related to the same Bacillus bacterium isolated from seeds germinated under sterile conditions, according to partial 16S rRNA sequences. Bright field and fluorescence imaging revealed bacteria present in the intercellular space of four-week-old tubers and in the sterile germinated seeds. Sectioning and imaging of the nodules show a central nodule vasculature and infected cells extending inwards to the main root vasculature. Nitrogen fixation in the plants was indirectly confirmed by acetylene reduction. Our results suggest P. esculentum has formed a unique symbiosis with a nitrogen fixing Bacillus bacterium that transmits vertically in the seeds and induces nodules.

Library of Congress Subject Headings

Legumes

Endophytes

Nitrogen -- Fixation

Plant-microbe relationships

Root-tubercles

Symbiosis

Description

Includes bibliographical references (pages 51--63)

Format

application/pdf

Number of Pages

87

Publisher

South Dakota State University

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Rights Statement

In Copyright