An Influence of Plant Growth Substances on Growth and Nitrogenase Activity from Azospirillum Brasiliense

Summary

Plant growth substances, such as auxins, cytocinin, gibberillin and abciscin were tested for their effect on growth and nitrogenase activity from batch culture grown Azospirillum brasilense. The present results indicate that Indol-3-acetic acid (IAA) and 6-benzyl-aminopurine (BAP) can have a stimulating influence on the bacterial growth. Treatments with gibberillin (GA) and IAA in a final concentration of 2,5 mg/1 are highly increasing the nitrogenase activity, while GA in a low concentration (0,025 mg/1) represses N₂ fixation. Comparing IAA, 2,4 D and 3,5 D with each other it could be demonstrated, that both, IAA and 2,4 D are positively effecting the nitrogen fixation, but 3,5 D does not. When tested for their effect on the NH ⁺₄ -repression of nitrogenase it is only GA with a slight derepressing effect and this only in its lowest concentration tested. This effect became stronger and statistical more serious, when the GA addition was combined with an abscisic acid (ABA) or IAA treatment. ABA itself did not show any effect.

In conclusion this paper will demonstrate, that nitrogen fixation of the rhizosphere bacteria Azospirillum could be influenced by plant produced growth substances, what may be at least important in the discussion over the kind of association that exists between gramineae plant and Azospirillum.