Plant-growth-promoting compounds produced by two agronomically important strains of <Emphasis Type="Italic">Azospirillum brasilense</Emphasis>, and implications for inoculant formulation |
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Authors: | D Perrig M L Boiero O A Masciarelli C Penna O A Ruiz F D Cassán M V Luna |
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Institution: | (1) Laboratorio de Fisiología Vegetal, Departamento de Ciencias Naturales, Facultad de Ciencias Exactas, Físico-Químicas y Naturales, Universidad Nacional de Río Cuarto, Campus Universitario, CP 5800 Río Cuarto, Córdoba, Argentina;(2) Departamento de Investigación y Desarrollo, Nitragin Argentina SA, Pilar, Buenos Aires, Argentina;(3) Instituto de Investigaciones Biológicas—Instituto Tecnológico de Chascomús, Buenos Aires, Argentina |
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Abstract: | We evaluated phytohormone and polyamine biosynthesis, siderophore production, and phosphate solubilization in two strains
(Cd and Az39) of Azospirillum brasilense used for inoculant formulation in Argentina during the last 20 years. Siderophore production and phosphate solubilization
were evaluated in a chemically defined medium, with negative results. Indole 3-acetic acid (IAA), gibberellic acid (GA3), and abscisic acid (ABA) production were analyzed by gas chromatography-mass spectrometry. Ethylene, polyamine, and zeatin
(Z) biosynthesis were determined by gas chromatography-flame ionization detector and high performance liquid chromatography
(HPLC-fluorescence and -UV), respectively. Phytohormones IAA, Z, GA3, ABA, ethylene, and growth regulators putrescine, spermine, spermidine, and cadaverine (CAD) were found in culture supernatant
of both strains. IAA, Z, and GA3 were found in all two strains; however, their levels were significantly higher (p < 0.01) in Cd (10.8, 2.32, 0.66 μg ml−1). ABA biosynthesis was significantly higher (p < 0.01) in Az39 (0.077 μg ml−1). Ethylene and polyamine CAD were found in all two strains, with highest production in Cd cultured in NFb plus l-methionine (3.94 ng ml−1 h−1) and Az39 cultured in NFb plus l-lysine (36.55 ng ml−1 h−1). This is the first report on the evaluation of important bioactive molecules in strains of A. brasilense as potentially capable of direct plant growth promotion or agronomic yield increase. Az39 and Cd showed differential capability
to produce the five major phytohormones and CAD in chemically defined medium. This fact has important technological implications
for inoculant formulation as different concentrations of growth regulators are produced by different strains or culture conditions. |
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Keywords: | Azospirillum Abscisic acid Gibberellic acid Indole 3-acetic acid Ethylene Cadaverine Plant-growth-promoting rhizobacteria |
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