Abstract
Bacterial production of indole-3-acetic acid (IAA) and its effects on plant growth have been frequently studied but there have been few studies on the ecology of IAA-degrading bacteria. In this study, among eight endophytic bacterial strains previously isolated from the same sweet potato sample including two IAA producers, Klebsiella sp. Sal 1 and Enterobacter sp. Sal 3, all of the strains showed IAA-degrading ability to some extent. Herbaspirillum sp. Sal 6 had the highest activity for IAA and tryptophan. When the IAA producers and the degrader were co-cultured in tryptophan-amended N+MR liquid medium, the concentrations of IAA decreased. Inoculation with Klebsiella sp. Sal 1, the highest IAA producer among the test strains, increased fresh root weight of tomato and radish, but the effect decreased by co-inoculation with IAA-degrading Herbaspirillum sp. Sal 6. Since both strains colonized plant parts at high populations, it was likely that the IAA degrader decreased IAA levels in the plants by degrading IAA and/or its precursor tryptophan. When IAA-producing biofertilizers are used, interactions with IAA degraders in plants should be considered.
Highlights
Indole-3-acetic acid (IAA) is an important substance that regulates different developmental processes in plants such as cell division, elongation, and differentiation, as well as responses to gravity and light
The concentration of indole-3-acetic acid (IAA) in plants is crucial for controlling their growth [1], and it is controlled through biosynthesis, conjugation, degradation and intercellular transport [2]
The application of IAA-producing bacteria to plants has shown significant increases in plant growth and yield as follows: Pseudomonas fluorescens and Bacillus subtilis in onion [8], Rahnella aquatilis in hybrid poplar [4], Enterobacter ludwigii in rice [9], and Klebsiella pneumonia in wheat and moth bean [10]
Summary
Indole-3-acetic acid (IAA) is an important substance that regulates different developmental processes in plants such as cell division, elongation, and differentiation, as well as responses to gravity and light. The application of IAA-producing bacteria to plants has shown significant increases in plant growth and yield as follows: Pseudomonas fluorescens and Bacillus subtilis in onion [8], Rahnella aquatilis in hybrid poplar [4], Enterobacter ludwigii in rice [9], and Klebsiella pneumonia in wheat and moth bean [10]. Most of these studies were conducted under controlled conditions and single strain inoculation. The aim of this study was to examine the IAA-degrading ability of these strains, and to elucidate the effects of co-inoculation of the IAA producers with an IAA degrader on plant growth
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