C2H2 and Ar induce rapid declines in nitrogenase activity and CO2 evolution in nodules of Datisca glomerata

Preliminary studies have indicated that after addiction of C2H2 there is a rapid decline in nitrogenase activity in the nodules of Datisca glomerata. The present work was undertaken to determine whether (1) there is also a decline in respiration and (2) the decline is associated with the cessation of ammonia production. The rates of C2H4 and CO2 evolution by nodulated root systems of Datisca were measured as a function of time after exposure to C2H2. The peak rate of C2H4 evolution occurred at 30 s after C2H2 exposure, while the rate of CO2 evolution started to decline at 60 s after exposure to C2H2. Incubation of nodules in a gas mixture containing Ar also caused a decline in CO2 evolution. Further, pretreatment with Ar eliminated most of the C2H2-induced decline in nitrogenase activity and CO2 evolution. These C2H2- and Ar-induced declines in Datisca nodules are more rapid than those reported in any other nodules. They are evidence that continued ammonia formation is essential for maintenance of normal nitrogenase activity in Datisca nodules.