Pump-leak sodium fluxes in low salt corn roots |
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Authors: | John M Cheeseman |
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Institution: | (1) Department of Botany, University of Illinois, 61801 Urbana, IL |
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Abstract: | Summary The influx and efflux of sodium from 4-hr washed, low salt corn roots (Zea mays L.) has been studied for characterization of passive and active components. Initial Na+ content of the roots is very low, 2.25±0.4 mol/g fresh weight. Na+ influx in the presence of 0.2mm Ca2+ and 0.002 to 20mm K+ is passive (a leak ) based upon Goldman-type models, being determined by Na+ and cell potential ( ). Na+ was not transported by the K+ carrier and influx was unaffected by 50 m dicyclohexylcarbodiimide (DCCD). Permeability of the cells to Na+ was of the same order asP
k.Efflux of Na+ was by an efficient and rapid active transport system (a pump ), thus accounting for the failure of these roots to accumulate high levels of Na+. In short-term loading and efflux experiments, internal Na+ turnover had a half-time of about 5 min. Sodium efflux was unaffected by DCCD. Net H+ flux was zero in the presence of DCCD regardless of sodium efflux, indicating absence of Na+/H+ antiport. Efflux of Na+ was equally rapid into medium containing no Na+ and only 0.002mm K+. K+ influx accounted for less than 4% of Na+ efflux, prompting the hypothesis that the Na+ (or cation?) efflux pump is the second electrogenic system previously defined based upon electrophysiological measurements. |
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Keywords: | Sodium Zea mays electrogenic pumps active transport roots DCCD pump-leak |
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