In the case of nonmetabolised ions, tracer retention in tissue after varying periods of elution can be used to characterise turnover, whereas, for metabolised ions, the rate of tracer release must be monitored ( Lee & Clarkson, 1986 ) and the chemical identity of the eluate must be confirmed ( Siddiqi et al., 1991 ).
Can unidirectional influx be measured in higher plants? A mathematical approach using parameters from efflux analysis
Article first published online: 1 AUG 2002
Volume 150, Issue 1, pages 37–47, April 2001
How to Cite
Britto, D. T. and Kronzucker, H. J. (2001), Can unidirectional influx be measured in higher plants? A mathematical approach using parameters from efflux analysis. New Phytologist, 150: 37–47. doi: 10.1046/j.1469-8137.2001.00080.x
2 The authors observed substantial decreases in ammonium fluxes when methionine sulphoximine (MSO)-treated barley plants were labelled for increasing lengths of time; however, interpretations of NH 4+ flux data under MSO treatment remain problematic and should not be used to establish mechanisms underlying transport ( Platt & Anthon, 1981 ; Feng et al., 1994 ; Kronzucker et al., 1995c ; Wieneke & Roeb, 1998 ).
3 Interestingly, in the case of inorganic nitrogen exchange, the apparent constancy of t ½ vis-à-vis changing conditions of N-suppy ( Kronzucker et al., 1995a,b ) renders this task somewhat simpler, but still necessitates measurements of efflux for the determination of flux ratio.
- Issue published online: 1 AUG 2002
- Article first published online: 1 AUG 2002
- Received: 10 July 2000Accepted: 23 October 2000
- compartmental analysis;
- k constant;
- steady state
- • A comprehensive and pragmatic approach to the design of unidirectional ion transport experiments in plants is presented here, revising and simplifying classical models.
- • The kinetic constant for cytosolic ion exchange ( kc ) is critical to the understanding of the interrelated flux processes occurring simultaneously at the cellular level. This constant is most effectively estimated using the compartmental analysis by efflux method, which, by providing values for additional kinetic parameters (i.e. unidirectional influx and efflux) can be used to determine the extent of distortion inherent in assessments of influx at, or close to, the steady state.
- • Focusing on the kinetics of nitrogen exchange, with tracer efflux experiments in barley ( Hordeum vulgare ) using 13NH4+, conducted under perturbation conditions, it was demonstrated that a transitional state was rapidly established following a concentration shift, characterized by a restoration of the preperturbational (steady-state) kc value. It is concluded that a reasonably accurate estimate of unidirectional influx can be made when influx measurements are conducted subsequent to the establishment of this transitional state.
- • A mathematical treatment of unidirectional flux processes allows the exact determination of errors caused by ionic counterfluxes under steady-state conditions.