The nitrate reductase and nitrite reductase activities in cucumber cucumis sativus cultivar monastyrski seedlings as affected on divalent cations

Buczek, J.

Acta Physiologiae Plantarum 2(3): 221-232


ISSN/ISBN: 0137-5881
Accession: 006724777

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The nitrate reductase (NR) activity in cotyledons of cucumber seedlings was inhibited after 24 h growth of plants in induction medium containing Ca(NO3)2 or Mg(NO3)2 salts; in roots the repression of NR activity took place only in the presence of Mg2+. The addition of K+ into these solutions, suppressed the inhibitory effect of Ca2+ on NR activity while the inhibitory effect of Mg2+ was somewhat lowered. Increasing concentrations of Ca2+ (from 1 to 10 mM) in induction medium containing 10 mM KNO3 were associated with increased rates of NR and nitrite reductase (NiR) activity and with absorption of NO3-; a positive correlation between increment of enzymes activity and absorption of NO3- has not been stated. NR activity and absorption of NO3- were decreased; and at the same time, the NiR activity increased when plants were grown in media with increasing concentration of Mg2+. The absorption of NO3- was not lowered in the presence of 1 mM Mg2+; and at the same time, the NR activity was inhibited by about 50%. Divalent cations may indirectly affect the activity of nitrate assimilatory enzymes by their influence on the distribution and translocation of NO3- and its reduced products.