NH4+-stimulated and -inhibited components of K+ transport in rice (Oryza sativa L.).
The disruption of K(+) transport and accumulation is symptomatic of NH(4)(+) toxicity in plants. In this study, the influence of K(+) supply (0.02-40 mM) and nitrogen source (10 mM NH(4)(+) or NO(3)(-)) on root plasma membrane K(+) fluxes and cytosolic K(+) pools, plant growth, and whole-plant K(+) distribution in the NH(4)(+)-tolerant plant species rice (Oryza sativa L.) was examined. Using the radiotracer (42)K(+), tissue mineral analysis, and growth data, it is shown that rice is affected by NH(4)(+) toxicity under high-affinity K(+) transport conditions. Substantial recovery of growth was seen as [K(+)](ext) was increased from 0.02 mM to 0.1 mM, and, at 1.5 mM, growth was superior on NH(4)(+). Growth recovery at these concentrations was accompanied by greater influx of K(+) into root cells, translocation of K(+) to the shoot, and tissue K(+). Elevating the K(+) supply also resulted in a significant reduction of NH(4)(+) influx, as measured by (13)N radiotracing. In the low-affinity K(+) transport range, NH(4)(+) stimulated K(+) influx relative to NO(3)(-) controls. It is concluded that rice, despite its well-known tolerance to NH(4)(+), nevertheless displays considerable growth suppression and disruption of K(+) homeostasis under this N regime at low [K(+)](ext), but displays efficient recovery from NH(4)(+) inhibition, and indeed a stimulation of K(+) acquisition, when [K(+)](ext) is increased in the presence of NH(4)(+).
Szczerba
Mark W
MW
Department of Biological Sciences, University of Toronto, 1265 Military Trail, Toronto, Ontario, Canada M1C 1A4.
Britto
Dev T
DT
Ali
Shabana A
SA
Balkos
Konstantine D
KD
Kronzucker
Herbert J
HJ
D003600:Cytosol / Q000378:metabolism; D017136:Ion Transport; D012275:Oryza / Q000378:metabolism*; D018517:Plant Roots / Q000378:metabolism; D011188:Potassium / Q000378:metabolism*; D000644:Quaternary Ammonium Compounds / Q000378:metabolism*
D000644:Quaternary Ammonium Compounds; D011188:Potassium