Effect of various nitrogen sources on growth and the nitrate-nitrite reductase system of the Azolla mexicana -Anabaena azollae symbiosis

Abstract

The nitrogen-fixing symbiosis of the fern Azolla mexicana Presl. and the blue-green algae, Anabaena azollae Strasburger will grow solely on atmospheric nitrogen and/or added nitrogen sources such as nitrate and ammonium forms. Comparisons of the effects of these nitrogen sources on growth and induction, levels of activity and stability of nitrate and nitrite reductase were made. Both in vivo and in vitro assays were employed. Growth was not significantly increased by addition of nitrate-nitrogen over that obtained on atmospheric nitrogen alone. Both sources, however, gave more growth than ammonium-nitrogen. Nitrate reductase and nitrite reductase levels were 79 nmol nitrite used g fresh weight −1 h −1 and 67 nmol nitrite used g fresh weight −1 h −1, respectively. Nitrate reductase, unlike nitrite reductase, required its substrate for induction. Nitrate, but not nitrite reductase was increased 17-fold by 1 ppm simazine. Neither nitrate nor nitrite induced nitrite reductase in the fern. The majority of the nitrate reductase was localized in the fern fronds; a small amount (20%) was found in the roots.