JXB Advance Access originally published online on January 30, 2004
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Journal of Experimental Botany, Vol. 55, No. 397, pp. 761-769, March 1, 2004
© 2004 Oxford University Press
Plants and the Environment |
Inhibition of nitrate influx by glutamine in Lolium perenne depends upon the contribution of the HATS to the total influx
Received 20 May 2003; Accepted 11 November 2003
The Macaulay Institute, Craigiebuckler, Aberdeen AB15 8QH, UK
* Fax: +44 (0)1224 311556. E-mail: b.thornton{at}macaulay.ac.uk
Plants of Lolium perenne L. were grown in sterile solution culture supplied with 2 mol m–3 nitrogen as either nitrate or ammonium. Glutamine at 5 mol m–3 was added to the nutrient solution of half the plants for 24 h. Root nitrate influx (at external nitrate concentrations 0–2000 mmol m–3) and amino acid concentrations were determined. In a second experiment the concentration of the added glutamine was varied from 0–5 mol m–3 and nitrate influx determined at 250 and 2000 mmol m–3. The maximum rate of influx attributed to the high affinity transport system (HATS) was reduced by 66% by the presence of glutamine achieved through an 84% reduction in its constitutive component and a 59% reduction in its inducible component. Influx attributed to LATS was unaffected by the addition of glutamine. The inhibition of total nitrate influx by glutamine was positively related to the contribution of HATS to the total influx. In both nitrate- and ammonium-grown plants, the concentration of glutamine required to inhibit nitrate influx significantly was lower when influx was determined at 250 mmol m–3 compared with 2000 mmol m–3 nitrate. The addition of glutamine increased its concentrations in root tissue. However, the results cannot be attributed to changes in glutamine alone as its addition also resulted in increased concentrations of other amino acids. Implications for plants growing under field conditions are discussed.
Key words: Glutamine, HATS, LATS, Lolium perenne, nitrate influx.
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