Comparative induction of nitrate reductase by nitrate and nitrite in barley leaves.
The comparative induction of nitrate reductase (NR) by ambient NO3- and NO2- as a function of influx, reduction (as NR was induced) and accumulation in detached leaves of 8-day-old barley (Hordeum vulgare L.) seedlings was determined.  The dynamic interaction of NO3- influx, reduction and accumulation on NR induction was shown.  The activity of NR, as it was induced, influenced its further induction by affecting the internal concentration of NO3-.  As the ambient concentration of NO3- increased, the relative influences imposed by influx and reduction on NO3- accumulation changed with influx becoming a more predominant regulant.  Significant levels of NO3- accumulated in NO2(-)-fed leaves.  When the leaves were supplied cycloheximide or tungstate along with NO2-, about 60% more NO3- accumulated in the leaves than in the absence of the inhibitors.  In NO3(-)-supplied leaves NR induction was observed at an ambient concentration of as low as 0.02 mM.  No NR induction occurred in leaves supplied with NO2- until the ambient NO2- concentration was 0.5 mM.  In fact, NR induction from NO2- solutions was not seen until NO3- was detected in the leaves.  The amount of NO3- accumulating in NO2(-)-fed leaves induced similar levels of NR as did equivalent amounts of NO3- accumulating from NO3(-)-fed leaves.  In all cases the internal concentration of NO3-, but not NO2-, was highly correlated with the amount of NR induced.  The evidence indicated that NO3- was a more likely inducer of NR than was NO2-.
Aslam
M
M
Plant Growth Laboratory and the Department of Agronomy and Range Science, University of California, Davis 95616, USA.
Rosichan
J L
JL
Huffaker
R C
RC
D003513:Cycloheximide / Q000494:pharmacology; D004790:Enzyme Induction / Q000187:drug effects; D005308:Fertilizers; D001467:Hordeum / Q000201:enzymology* / Q000378:metabolism; D009565:Nitrate Reductases / Q000096:biosynthesis*; D009566:Nitrates / Q000378:metabolism / Q000494:pharmacology*; D009573:Nitrites / Q000378:metabolism / Q000494:pharmacology*; D018515:Plant Leaves / Q000187:drug effects / Q000201:enzymology* / Q000378:metabolism; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D000644:Quaternary Ammonium Compounds / Q000494:pharmacology; D017973:Tungsten Compounds / Q000494:pharmacology; D014508:Urea / Q000494:pharmacology
D005308:Fertilizers; D009566:Nitrates; D009573:Nitrites; D011500:Protein Synthesis Inhibitors; D000644:Quaternary Ammonium Compounds; D017973:Tungsten Compounds; D014508:Urea; D003513:Cycloheximide; D009565:Nitrate Reductases; C045951:tungstate