Verification of Nitrogenase Activity (C₂h₂ Reduction) in Azospirillum Populated, 2,4-Dichlorophenoxyacetic Acid Induced, Root Structures of Wheat

Abstract

The characteristics of C₂H₄ formation and H₂ evolution associated with 2,4-D induced root structures on wheat seedlings inoculated with Azospirillum brasilense Sp7 have been investigated. C₂H₄ formation and H₂ evolution with 2,4-D treatment is several times greater than that by wheat seedlings inoculated with Azospirillum alone, as the result of the formation of a niche for azospirilla protected from O₂. This increased C₂H₄ production in 2,4-D treated seedlings was proportional to C₂H₂ concentration and it was strongly inhibited by nitrite and ammonia. The inhibition increased with greater ammonia and nitrite concentration, but was reversible. The increased rate of C₂H₂ reduction activity was correlated with ¹⁵N enrichment in 2,4-D treated seedlings. These results confirm that the C₂H₄ formation was C₂H₂ dependent and represented the nitrogenase activity of A. brasilense associated with the 2,4-D induced root structures of wheat seedlings rather than C₂H₂ produced by plant tissues.