VERIFICATION OF NITROGENASE ACTIVITY (C2H2 REDUCTION) IN AZOSPIRILLUMPOPULATED, 2,4-DICHLOROPHENOXYACETIC ACID-INDUCED, ROOT STRUCTURES OFWHEAT

The characteristics of C2H4 formation and H-2 evolution associated wit h 2,4-D induced root structures on wheat seedlings inoculated with Azo spirillum brasilense Sp7 have been investigated. C2H4 formation and H- 2 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 incre ased C2H4 production in 2,4-D treated seedlings was proportional to C2 H2 concentration and it was strongly inhibited by nitrite and ammonia. The inhibition increased with greater ammonia and nitrite concentrati on, but was reversible. The increased rate Of C2H2 reduction activity was correlated with N-15 enrichment in 2,4-D treated seedlings. These results confirm that the C2H4 formation was C2H2 dependent and represe nted the nitrogenase activity of A. brasilense associated with the 2,4 -D induced root structures of wheat seedlings rather than C2H4 produce d by plant tissues.