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Appl Environ Microbiol. 1987 May; 53(5): 1051-1055
Copyright © 1987, American Society for Microbiology. All Rights Reserved.

Influence of 5-Methyltryptophan-Resistant Bradyrhizobium japonicum on Soybean Root Nodule Indole-3-Acetic Acid Content {dagger}

William J. Hunter

Soil-Plant Nutrient Research Unit, Agricultural Research Service, U.S. Department of Agriculture, Fort Collins, Colorado 80522

ABSTRACT

Bradyrhizobium japonicum mutants resistant to 5-methyltryptophan were isolated. Some of these mutants were found to accumulate indole-3-acetic acid (IAA) and tryptophan in culture. In greenhouse studies, nodules from control plants inoculated with wild-type bradyrhizobia contained 0.04, 0.10, and 0.58 µg of free, ester-linked, and peptidyl IAA g (fresh weight) of nodules–1, respectively. Nodules from plants inoculated with 5-methyltryptophan-resistant bradyrhizobia contained 0.94, 1.30, and 10.6 µg of free, ester-linked, and peptidyl IAA g (fresh weight) of nodules–1, respectively. This manyfold increase in nodule IAA content indicates that the Bradyrhizobium inoculum can have a considerable influence on the endogenous IAA level of the nodule. Further, these data imply that much of the IAA that accumulated in the high-IAA-containing nodules was of bacterial rather than plant origin. These high-IAA-producing 5-methyltryptophan-resistant bacteria were poor symbiotic nitrogen fixers. Plants inoculated with these bacteria had a lower nodule mass and fixed less nitrogen per gram of nodule than did plants inoculated with wild-type bacteria.

FOOTNOTES

{dagger} Contribution of Agricultural Research Service, U.S. Department of Agriculture, in cooperation with the Colorado State University Experiment Station.

Appl Environ Microbiol. 1987 May; 53(5): 1051-1055
Copyright © 1987, American Society for Microbiology. All Rights Reserved.





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Copyright © 1987 by the American Society for Microbiology. All rights reserved.