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

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.