Effect of pH and calcium on short-term NO3- fluxes in roots of barley seedlings.
The effect of pH and Ca2+ on net NO3- uptake, influx, and efflux by intact roots of barley (Hordeum vulgare L.) seedlings was studied. Seedlings were induced with NO3- or NO2-. Net NO3- uptake and efflux, respectively, were determined by following its depletion from, and accumulation in, the external solution. Since roots of both uninduced and NO2(-)-induced seedlings contain little internal NO3- initial net uptake rates are equivalent to influx (M. Aslam, R.L. Travis, R.C. Huffaker [1994] Plant Physiol 106: 1293-1301). NO3-, uptake (influx) by these roots was little affected at acidic pH. In contrast, in NO3(-)-induced roots, which accumulate NO3-, net uptake rates decreased in response to acidic pH. Under these conditions, NO3- efflux was stimulated and was a function of root NO3- concentration. Conversely, at basic pH, NO3-  uptake by NO3- and NO2(-)-induced and uninduced roots decreased, apparently because of the inhibition of influx. Calcium had little effect on NO3- uptake (influx) by NO2(-)-induced roots at either pH 3 or 6. However, in NO3(-)-induced roots, lack of Ca2+ at pH 3 significantly decreased net NO3- uptake and stimulated efflux. The results indicate that at acidic pH the decrease in net NO3- uptake is due to the stimulation of efflux, whereas at basic pH, it is due to the inhibition of influx.
Aslam
M
M
Department of Agronomy and Range Science, University of California, Davis 95616, USA.
Travis
R L
RL
Huffaker
R C
RC
D002118:Calcium / Q000494:pharmacology*; D002133:Calcium Sulfate / Q000494:pharmacology; D001467:Hordeum / Q000187:drug effects / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D009566:Nitrates / Q000378:metabolism* / Q000493:pharmacokinetics / Q000494:pharmacology; D009573:Nitrites / Q000378:metabolism; D018517:Plant Roots / Q000187:drug effects* / Q000378:metabolism; D017680:Potassium Compounds / Q000494:pharmacology; D013997:Time Factors
D009566:Nitrates; D009573:Nitrites; D017680:Potassium Compounds; C023844:potassium nitrate; D002118:Calcium; D002133:Calcium Sulfate