Abstract
Background: It is assumed that plant growth regulators produced by beneficial bacterial species could also influence plant growth. IAA is a major plant growth regulator responsible for stimulation of plant growth. There are several microorganisms which are naturally responsible for L- tryptophan metabolism. Methods: In total, 56 indigenous morphologically distinct isolates from rice roots were selected and subsequently characterized with biochemical tests, 16S rRNA sequencing and plant growth promoting activities. Pseudomonasfluorescens RE1 (GenBank: MF102882.1) and RE17 (GenBank: MF103672.1) endophytes resulted in better PGP activity against the other 54 isolates. Both endophytes were tested to screen indole-3-acetic acid production ability in pure culture conditions with L-tryptophan at 0, 50, 100, 200 and 500µg/ml concentrations. Results: P.fluorescens RE1 was recorded efficient for indole production in comparison to P. fluorescens RE17 at various L-tryptophan concentrations. P. fluorescens RE1 was shown to produce between 0.8 µg/ml and 11.5µg/ml of indole at various tryptophan concentrations, while RE17 produced between 1.2µg/ml and 10.2µg/ml. At 200 and 500µg/ml tryptophan concentration, P. fluorescens RE17 produced 7.4pmol/ml and 9.3pmol/ml IAA, respectively. Conclusions: Inoculation of maize seed with P. fluorescens RE1 and RE17 showed a significantly higher level of IAA production in comparison to non-inoculated seeds. Current study outcomes proved that plant growth regulators produced by Pseudomonas species could also play a critical role in plant growth promotion.
Highlights
Indole-3-acetic acid (IAA) is one of the most physiologically active phytohormones, and is a product of L-tryptophan metabolism (Yu et al, 2017). 80% of rhizospheric microorganisms naturally yield auxins as secondary metabolites due to the rich supplies of root exudates (Myresiotis et al, 2015)
When 200μg/ml of L-tryptophan was added to the medium, RE1 and RE17 produced eight, and three times the concentration of indole produced at 50μg/ml of L-tryptophan concentration, respectively (Figure 2)
Current studies examine IAA generating endophytic P. fluorescens strains from rice roots, with many reporting the active role of tryptophan in the production of IAA by plant growth promoting bacteria (Karnwal, 2017; Stachecki et al, 2004)
Summary
Indole-3-acetic acid (IAA) is one of the most physiologically active phytohormones, and is a product of L-tryptophan metabolism (Yu et al, 2017). 80% of rhizospheric microorganisms naturally yield auxins as secondary metabolites due to the rich supplies of root exudates (Myresiotis et al, 2015). The rhizosphere is a highly selective area for host-microbe interaction, and during their life span few microbes may enter inside the plant tissue and stay without causing any negative symptoms (Santoyo et al, 2016) These indigenous colonizers reside in almost all internal tissues/cells of plant ranging from tissues of the roots to stem, leaf, flower, fruit and seed (Souza et al, 2015). Methods: In total, 56 indigenous morphologically distinct isolates from rice roots were selected and subsequently characterized with biochemical tests, 16S rRNA sequencing and plant growth promoting activities. Pseudomonas fluorescens RE1 (GenBank: MF102882.1) and RE17 (GenBank: MF103672.1) endophytes resulted in better PGP activity against the other 54 isolates Both endophytes were tested to screen indole-3-acetic acid production ability in pure culture conditions with L-tryptophan at 0, 50, 100, 200 and 500μg/ml concentrations. Current study outcomes proved that plant growth regulators produced by Pseudomonas species could play a critical role in plant growth promotion
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