| dc.description.abstract |
Exposure of the N2-fixing cyanobacterium Anabaena BT2 to ultraviolet-B radiation (2.5 W
m 2) for 30 min resulted in complete loss of nitrogenase activity but 100% cell killing occurred only after
a 90-min exposure. Inactivation of nitrogenase activity was not specific to Anabaena BT2; other species
also showed a similar effect. The time required for 100% killing and inactivation of nitrogenase activity
differed in various species, and this difference may be ascribed to the presence of different levels of
UV-B protection mechanisms in individual species. Inhibition of nitrogenase activity was immediate,
since exposure of cultures to UV-B for as little as 5 min elicited some inhibition of activity. The activity
of UV-B-inhibited nitrogenase did not recover upon transfer of exposed cells to fluorescent light,
suggesting that the inhibition may be due to specific inactivation of the enzyme. By employment of
inhibitors of protein synthesis and PS-II activity, it was demonstrated that restoration of nitrogenase
activity in a UV-B-treated culture occurred by fresh synthesis of nitrogenase polypeptide. Our findings
suggest that estimation of nitrogenase activity in diazotrophic species may be used as a marker enzyme
for assessing the impact of UV-B radiation. |
en_US |