P. Mateo et al., O-2-INDUCED INACTIVATION OF NITROGENASE AS A MECHANISM FOR THE TOXIC ACTION OF CD2-208( ON NOSTOC UAM), New phytologist, 126(2), 1994, pp. 267-272
Direct involvement of Cd2+ in the inhibition of N-2 fixation in Nostoc
UAM 208 has been investigated. Significant inhibition of nitrogenase
activity was detected 2 h after addition of Cd2+ to the culture medium
. Under anaerobic conditions the inhibitory effect of Cd2+ was largely
prevented, suggesting that this ion induced inactivation of nitrogena
se by O-2. Addition of Ca2+ to Cd2+-treated cultures markedly decrease
d the inhibition of nitrogenase activity, and this amelioration of Cd2
+ toxicity was dose-dependent, indicating an antagonistic interaction
between the two ions. Ultrastructural examination of cultures treated
with Cd2+ showed heterocyst deterioration and a decrease in the cohesi
veness of the polysaccharide layer of the heterocyst envelope. A possi
ble antagonistic relationship between Ca2+ and Cd2+ in terms of the O-
2-mediated inhibition of N-2 fixation is discussed.