Protoplast ion fluxes: their measurement and variation with time, position and osmoticum |
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Authors: | Sergey Shabala Ian Newman John Whittington Unggul Juswono |
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Affiliation: | (1) Department of Physics, University of Tasmania, GPO Box 252-21, Hobart, Tas 7001, Australia, AU;(2) The Murray-Darling Freshwater Research Centre and CRC for Freshwater Ecology, PO Box 921, Albury, NSW 2640, Australia, AU;(3) Jurusan Fisika, FMIPA, Universitas Brawijaya, Malang 65145, Indonesia, ID |
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Abstract: | The ability to measure directly individual protoplast ion fluxes is a valuable addition to patch clamp and other techniques when using protoplasts to study membrane transporters. Before interpreting observations on protoplasts in terms of behaviour of intact cells and tissues, some methodological questions should be addressed. These include effects of space and time variations of transporter activities over the membrane, the osmotic dependence of specific ion transporters and the effect of the regenerating cell wall. In this study net H+ and Ca2+ fluxes were measured from individual corn (Zea mays L.) coleoptile protoplasts using a non-invasive microelectrode technique for ion flux measurements. For Ca2+, the flux distribution was almost symmetrical, ranging ±30 nmol · m−2 · s−1 around zero. For H+ it was skewed towards efflux ranging from −100 to +10 nmol · m−2 · s−1. The distribution of H+ fluxes through the protoplast surface was a complex mosaic which changed with time, sometimes showing oscillations. These flux variations with time and position around the surface, apparently driven by endogenous mechanisms, may be relevant to protoplast pH homeostasis. When the new cell wall was partially regenerated on the next day, the correlation between H+ and Ca2+ fluxes increased, which is consistent with the weak-acid Donnan-Manning model of cell wall ion exchange. Received: 11 June 1997 / Accepted: 10 July 1997 |
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Keywords: | : Calcium Membrane fluxes Oscillation (H+ flux) Proton Protoplast Zea (ion fluxes) |
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