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Research article2003Peer reviewed

Nitrogenase activity and root nodule metabolism in response to O-2 and short-term N-2 deprivation in dark-treated Frankia-Alnus incana plants

Lundquist, PO; Nasholm, T; Huss-Danell, K

Abstract

Inhibition of nitrogenase (EC 1.18.6.1) activity by O-2 has been suggested to be an early response to disturbance in carbon supply to root nodules in the Frankia-Alnus incana symbiosis. Intact nodulated root systems of plants kept in prolonged darkness of 22 h were used to test responses to O-2 and short-term N-2 deprivation (1 h in Ar:O-2). By using a Frankia lacking uptake hydrogenase it was possible to follow nitrogenase activity over time as H-2 evolution in a gas exchange system. Respiration was simultaneously recorded as CO2 evolution. Dark-treated plants had lower initial nitrogenase activity in N-2: O-2 (68% of controls), which declined further during a 1-h period in the assay system in N-2:O-2 at 21 and 17% O-2, but not at 13% O-2. When dark-treated plants were deprived of N-2 at 21 and 17% O-2 nitrogenase activity declined rapidly to 61 and 74%, respectively, after 20 min, compared with control plants continuously kept in their normal light regime. In contrast, there was no decline in dark-treated plants at 13% O-2, and only a smaller and temporary decline in control plants at 21% O-2. When dark-treated plants were kept at 21% O-2 during 45 min prior to N-2 deprivation at 17% O-2 the decline was abolished. This supports the idea that the decline in nitrogenase activity observed in N-2:O-2 at 21% O-2 and during N-2 deprivation was caused by O-2, which affected a sensitive nodule fraction. Nodule contents of the amino acids Gln and Cit decreased during N-2 deprivation, suggesting decreased assimilation of NH4+. Contents of ATP and ADP in nodules were not affected by short-term N-2 deprivation. ATP/ADP ratios were about 5 indicating a highly aerobic metabolism in the root nodule. We conclude that nitrogenase activity of Alnus plants exposed to prolonged darkness becomes more sensitive to inactivation by O-2. It seemed that dark-treated plants could not adjust their nodule metabolism at higher perceived pO(2) and during cessation of NH4+ production

Keywords

symbiosis; actinorhiza; Frankia; Alnus incana; root nodule; nitrogenase; oxygen protection; gas exchange; hydrogen evolution; respiration; citrulline; amino acid; adenylate

Published in

Physiologia Plantarum
2003, volume: 119, number: 2, pages: 244-252
Publisher: BLACKWELL MUNKSGAARD

SLU Authors

UKÄ Subject classification

Forest Science
Agricultural Science
Renewable Bioenergy Research

Publication identifier

  • DOI: https://doi.org/10.1034/j.1399-3054.2003.00177.x

Permanent link to this page (URI)

https://res.slu.se/id/publ/1688