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Ammonium fluxes into plant roots: Energetics, kinetics and regulation
Author(s) -
Glass Anthony D. M.,
Erner Yair,
Kronzucker Herbert J.,
Schjoerring Jan K.,
Siddiqi M. Yaeesh,
Wang M.Yuan
Publication year - 1997
Publication title -
zeitschrift für pflanzenernährung und bodenkunde
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.644
H-Index - 87
eISSN - 1522-2624
pISSN - 0044-3263
DOI - 10.1002/jpln.19971600220
Subject(s) - ammonium , kinetics , chemistry , permeation , biophysics , membrane , biochemistry , biology , physics , organic chemistry , quantum mechanics
Ammonium uptake across the plasma membranes of seedling roots of intact rice plants is thermodynamically active at low external concentrations, and consequently, electrogenic uniport is an unlikely mechanism for influx. At higher NH 4 + concentrations uptake is passive and electrogenic uniport is a possibility. While passive permeation of NH 3 is also possible at high external [NH 4 + ], influx measurements at 10 mM NH 4 + demonstrated a pH dependence which was inconsistent with significant NH 3 permeation. Kinetic studies using 13 NH 4 + established that influx at low external [H 4 + ] occurred via high affinity transport systems (HATS) in rice and spruce, while at higher [NH 4 + ], influx was mediated by low affinity transport systems (LATS), that showed linear concentration dependence. Ammonium influx via the HATS was shown to be up‐regulated or down‐regulated in response to changes of N status, whereas influx in the LATS was insensitive to N status. The identity or identities of the regulatory signals responsible for controlling influx are discussed.