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Multiphasic uptake of potassium by barley roots of low and high potassium content: Separate sites for uptake and transitions
Author(s) -
NISSEN PER
Publication year - 1980
Publication title -
physiologia plantarum
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.351
H-Index - 146
eISSN - 1399-3054
pISSN - 0031-9317
DOI - 10.1111/j.1399-3054.1980.tb03241.x
Subject(s) - potassium , hordeum vulgare , chemistry , diffusion , flux (metallurgy) , kinetics , ion , isotopes of potassium , allosteric regulation , biophysics , crystallography , biochemistry , botany , biology , poaceae , enzyme , thermodynamics , physics , organic chemistry , quantum mechanics
In the range 10 −6 M ‐ 5 × 10 −2 M uptake of K + in excised roots of barley ( Hordeum vulgare L. cv. Herta) with low and high K content could in both cases be represented by an isotherm with four phases. Uptake, especially in the range of the lower phases, was reduced in high K roots through decreases in V max and increases in K m . Similar data for other plants are also shown to be consistent with multiphasic kinetics. The concentrations at which transitions occurred were not affected by the K status, indicating the existence of separate uptake and transition sites. Uptake was markedly reduced in the presence of 10 −5 M 2,4‐dinitrophenol, especially at low K + concentrations, but the isotherms remained multiphasic. This contraindicates major contributions from a non‐carrier‐mediated, passive flux. A tentative hypothesis for multiphasic ion uptake envisions a structure which changes conformation as a result of all‐or‐none changes in a separate transition site. The structure is “tight” at low external ion concentrations (low V max . low K m . active uptake, allosteric regulation) and “loose” at high concentrations (high V max‐ high K m‐ facilitated diffusion, no regulation).