Enhanced Auxin Production by Azospirillum Pure Cultures from Plant Root Exudates

Authors
M. J. Mehdipour Moghadam 1
G. Emtiazi 1
Z. Salehi 2
1 Department of Biology, Faculty of Science, University of Isfahan, Isfahan, Islamic Republic of Iran.
2 Department of Biology, Faculty of Science, University of Guilan, Rasht, Islamic Republic of Iran.
Abstract
Bacteria of the genus Azospirillum are well known as plant growth promoting rhizobacteria. The ability to synthesize phytohormones is considered one of the most important mechanisms to promote plant growth and is widely distributed among plant-associated rhizobacteria.The most important phytohormone produced by Azospirillum is the auxin indole-3-acetic acid, with the L-tryptophan as the precursor. In the present study, we evaluate the capacity of eight Azospirillum strains isolated from rice and wheat, to produce in vitro auxins using plant exudates. Our results show that isolates produced auxins in tryptophan free media, but, generally, the amount produced increased when the tryptophan concentration increased. Some plants root exudates had a similar effect to tryptophan for the auxin production. In this sense, bean, rice and canola root extracts produced, respectively, 93.3%, 96.2%, and 88.31% more auxin than L-tryptophan. Azospirillum sp. isolate A3 had the maximal capacity to produce auxin. Therefore, the effect of cell free supernatant was studied on rice root development. Statistical analysis did not show any significant difference between root number and dry weight of the treated and control seedlings. However, significant differences were observed in root length and wet weight at α=0.01 and α=0.05, respectively.

Keywords

1. Akbari, G. A., Arab, S. M, Alikhani, H. A, Allahdadi, I. and Arzanesh, M. H. 2007. Isolation and Selection of Indigenous Azospirillum Spp. And the IAA of Superior Strains Effects on Wheat Roots. World J. Agr. Sci., 3: 523-529.
2. Bashan, Y., Holguin G. and Bashan, L. D. 2004. Azospirillum–plant Relationships: Physiological, Molecular, Agricultural, and Environmental Advances. Can. J. Microbiol., 50: 521–577.
3. Bent, E., Tuzun, S., Chanway, C. and Enebak, S. 2001. Alternation in Plant Growth and in Root Hormone Levels of Lodge Pole Pines Inoculated with Rhizobacteria. Can. J. Microbiol., 47: 793-800.
4. Bric, J. M., Bostok, R. M. and Silverstone, S.A. 1991. Rapid in Situ Assay for Indoleacetic Acid Production by Bacteria Immobilized on a Nitrocellulose Membrane. Appl. Environ. Microbiol., 57: 535-538.
5. Crozier, A., Arruda, P., Jasmim, J. M., Monteiro, M. and Sandberg, G. 1988. Analysis of Indole-3-Acetic Acid and Related Indoles in Culture Media from Azospirillum lipoferum and Azospirillum brasilense. Appl. Environ. Microbiol., 54: 2833-2837.
6. El-Khawas, H. and Adachi, K. 1999. Identification and Quantification Of Auxins in Culture Media of Azospirillum and Klebsiella and Their Effect on Rice Roots. Biol. Fertil. Soils, 28: 377–381.
7. Gadagi, R. S., Krishnaraj, P. U., Kulkarni, J. H. and Tongmin, S. 2003. The Effect of Combined Azospirillum Inoculation and Nitrogen Fertilizer on Plant Growth Promotion and Yield Response of the Blanket Flower Gaillardia pulchella. Sci. Hortic., 100: 323–332.
8. Gliesche, C.G., Menzel, M. and Fesefeldt, A. 1997. A Rapid Method for Creating Species-Specific Gene Probes for Methylotrophic Bacteria. J. Microbiol. Meth., 28: 25-34.
9. Gunarto, L., Adachi, K. and Senboku, T. 1999. Isolation and Selection of Indigenous Azospirillum Spp. from a Subtropical Island and Effect of Inoculation on Growth of Lowland Rice under Several Levels of N Application. Biol. Fertil. Soils, 28: 129–135.
10. Harari, A., Kigel, J. and Okon, Y. 1988. Involvement of IAA in the Interaction Between Azospirillum Brasilense and Panicum Miliaceum Roots. Plant Soil, 110: 275-282.
11. Kravchenko, L. V., Azarova, T. S., Makarova N. M. and Tikhonovich, I. A. 2004. The Effect of Tryptophan Present in Plant Root Exudates on the Phytostimulating Activity of Rhizobacteria. Microbiology, 73: 156-158.
12. Krieg, N. R. and Döbereiner, J. 1984. Genus Azospirillum. In: Bergey's Manual of Systematic Bacteriology. N.R. Krieg (ed.), Vol. 1: 94-104. Williams & Wilkins, Baltimore.
13. Okon, J. 1985. Azospirillum as a Potential Inoculant for Agriculture. Trends Biotech., 3: 223-228.
14. Perrig, D., Boiero, L., Masciarelli, O., Penna, C., Ruíz, O., Cassán F. and Luna V. 2007. Plant Growth Promoting Compounds Produced by two Agronomically Important Strains of Azospirillum Brasilense, and Their Implications for Inoculant Formulation. Appl. Microbial. Biotech., 75:1143–1150.
15. Steenhoudt, O. and Vanderleyden, J. 2000. Azospirillum, a Free-Living Nitrogen-Fixing Bacterium Closely Associated with Grasses: Genetic, Biochemical and Ecological Aspects. FEMS Microbiol. Rev., 24: 487-506.
16. Zakharova, E. A., Shcherbakov, A. A., Brudnik, V. V., Skripko, N. G., Bulkhin, N. S. and Ignatov, V. V. 1999. Biosynthesis of Indole-3-Acetic Acid in Azospirillum Brasilense. Insights from Quantum Chemistry. Eur. J. Biochem., 259: 572-576.
Journal of Agricultural Science and Technology
Volume 14, Issue 5
September and October 2012
Pages 985-994