Optimization of ammonium acquisition and metabolism by potassium in rice (Oryza sativa L. cv. IR-72).
ABSTRACT We present the first characterization of K(+) optimization of N uptake and metabolism in an NH(4)(+)-tolerant species, tropical lowland rice (cv. IR-72). (13)N radiotracing showed that increased K(+) supply reduces futile NH(4)(+) cycling at the plasma membrane, diminishing the excessive rates of both unidirectional influx and efflux. Pharmacological testing showed that low-affinity NH(4)(+) influx may be mediated by both K(+) and non-selective cation channels. Suppression of NH(4)(+) influx by K(+) occurred within minutes of increasing K(+) supply. Increased K(+) reduced free [NH(4)(+)] in roots and shoots by 50-75%. Plant biomass was maximized on 10 mm NH(4)(+) and 5 mm K(+), with growth 160% higher than 10 mm NO(3)(-)-grown plants, and 220% higher than plants grown at 10 mm NH(4)(+) and 0.1 mm K(+). Unlike in NH(4)(+)-sensitive barley, growth optimization was not attributed to a reduced energy cost of futile NH(4)(+) cycling at the plasma membrane. Activities of the key enzymes glutamine synthetase and phosphoenolpyruvate carboxylase (PEPC) were strongly stimulated by elevated K(+), mirroring plant growth and protein content. Improved plant performance through optimization of K(+) and NH(4)(+) is likely to be of substantial agronomic significance in the world's foremost crop species.
Department of Biological Sciences, University of Toronto, 1265 Military Trail, Toronto, Ontario, Canada.
Konstantine D
KD
Balkos
Dev T
DT
Britto
Herbert J
HJ
Kronzucker
D002462:Cell Membrane / Q000378:metabolism; D005974:Glutamate-Ammonia Ligase / Q000378:metabolism; D007473:Ion Channels / Q000378:metabolism; D009590:Nitrogen Radioisotopes; D012275:Oryza / Q000254:growth & development / Q000378:metabolism*; D010730:Phosphoenolpyruvate Carboxylase / Q000378:metabolism; D018517:Plant Roots / Q000378:metabolism; D018520:Plant Shoots / Q000378:metabolism; D011188:Potassium / Q000378:metabolism*; D000644:Quaternary Ammonium Compounds / Q000378:metabolism*
D007473:Ion Channels; D009590:Nitrogen Radioisotopes; D000644:Quaternary Ammonium Compounds; D010730:Phosphoenolpyruvate Carboxylase; D005974:Glutamate-Ammonia Ligase; D011188:Potassium