Acetylene- and argon-induced declines in nitrogenase activity in Coriaria arborea

Abstract

When assayed in a continuous flow system, 4-month-old Coriaria arborea plants underwent a decline in nitrogenase activity and nodule respiration upon exposure to acetylene (C 2H 2) (10 kPa). Neither nitrogenase nor respiratory activity was recovered following initial exposure and instead a new equilibrium level was reached. It is suggested C 2H 2-induced declines in Coriaria can be explained by a variable nodule diffusion resistance mechanism. The size of the decline in nitrogenase activity was reduced with increasing plant age such that 12-month old plants had a barely detectable decline. Prior adaptation to non-atmospheric pO 2 concentrations also affected the size of the decline. At 35 kPa O 2 the decline was significantly smaller than at 21 kPa O 2 but at 12 kPa O 2 the extent of the decline was greater. Both the effect of plant age and pO 2 on the C 2H 2-induced decline offer support to the operation of a variable diffusion resistance mechanism. Coriaria also underwent a decline in respiratory activity when Ar replaced N 2 in the assay gas stream. Lag-phase measurements showed the Ar-induced decline was accompanied by an increase in nodule diffusion resistance.