Nutrient Uptake and Organic Acid Anion Metabolism in Lupins and Peas Supplied with Nitrate

Unlike many plants reported in the literature, lupins do notexcrete OH^- in amounts equivalent to the net excess of inorganicanion uptake over inorganic cation uptake. To investigate themechanisms involved in the maintenance of charge balance, nutrientuptake and organic anion accumulation of lupins and peas suppliedwith a range of NO^-₃ concentrations, were compared. Lupins absorbed less NO^-₃ than peas on a dry weight basis, whichlargely accounted for the smaller excess of anion uptake overcation uptake in lupins than in peas at the same NO^-₃ supply.When anion uptake exceeded cation uptake, peas excreted an equivalentcharge of OH^-, whereas lupins excreted much smaller amountsof OH^- than the excess of anion over cation uptake. It was calculatedthat lupins excreted significant amounts of organic anions whenanion uptake exceeded cation uptake, whereas organic anion excretionfrom peas was negligible, regardless of their NO^-₃ supply andcation-anion balance. In this study, organic anion excretion was measured from lupinroots grown in near-sterile conditions while supplied with NO^-₃at 0, 500 and 2000 µM. Although complete sterility wasnot achieved, there was close agreement between the organicanion excreted and the excess anion over cation uptake.Copyright1994, 1999 Academic Press Lupinus angustifolius L., Pisum sativum L., organic acid, nutrient uptake