Ammonium can stimulate nitrate and nitrite reductase in the absence of nitrate in Clematis vitalba

• Published in: Plant, cell and environment Vol. 22; no. 7; pp. 859 - 866
• Main Authors: Bungard, R.A, Wingler, A, Morton, J.D, Andrews, M, Press, M.C, Scholes, J.D
• Format: Journal Article
• Language: English
• Published: Oxford, UK Oxford, UK : Blackwell Publishing Ltd 01.07.1999; Blackwell Publishing Ltd; Blackwell; Wiley Subscription Services, Inc
• Subjects: ammonium; ammonium compounds; Biological and medical sciences; chemical constituents of plants; Clematis vitalba; enzyme activity; Fundamental and applied biological sciences. Psychology; glutamate-ammonia ligase; glutamine synthetase; Hordeum vulgare; leaves; Metabolism; Nicotiana tabacum; nitrate; nitrate reductase; nitrates; nitrite reductase; nitrogen; Nitrogen metabolism; nutrient solutions; nutrient sources; nutrient uptake; Plant physiology and development; protein synthesis; shoots; substrates; Ammonium; Carbon-nitrogen ligases; Nutrition; Enzyme; Growth; Nitrite reductase; Ranunculaceae; Nitrates; Nitrogen; Metabolism; Enzymatic activity; Ligases; Nitrate reductase; Protein synthesis; Dicotyledones; Hydroponic cultivation; Angiospermae; Above ground plant part; Spermatophyta; Oxidoreductases; Glutamate-ammonia ligase
• ISSN: 0140-7791; 1365-3040
• DOI: 10.1046/j.1365-3040.1999.00456.x

Nitrogen assimilation was studied in the deciduous, perennial climber Clematis vitalba. When solely supplied with NO₃⁻ in a hydroponic system, growth and N-assimilation characteristics were similar to those reported for a range of other species. When solely supplied with NH₄⁺, however, nitrate reductase (NR) activity dramatically increased in shoot tissue, and particularly leaf tissue, to up to three times the maximum level achieved in NO₃⁻ supplied plants. NO₃⁻ was not detected in plant material that had been solely supplied with NH₄⁺, there was no NO₃⁻ contamination of the hydroponic system, and the NH₄⁺-induced activity did not occur in tobacco or barley grown under similar conditions. Western Blot analysis revealed that the induction of NR activity, either by NO₃⁻ or NH₄⁺, was matched by NR and nitrite reductase protein synthesis, but this was not the case for the ammonium assimilation enzyme glutamine synthetase. Exposure of leaf disks to N revealed that NO₃⁻ assimilation was induced in leaves directly by NO₃⁻ and NH₄⁺ but not glutamine. Our results suggest that the NH₄⁺-induced potential for NO₃⁻ assimilation occurs when externally sourced NH₄⁺ is assimilated in the absence of any NO₃⁻ assimilation. These data show that the potential for nitrate assimilation in C. vitalba is induced by a nitrogenous compound in the absence of its substrate and suggest that NO₃⁻ assimilation in C. vitalba may have a significant role beyond the supply of reduced N for growth.