Osmotic sensitivity of Ca2+ and H+ transporters in corn roots: effect on fluxes and their oscillations in the elongation region.
Seedling roots of corn were treated with different concentrations of mannitol-containing solution for 1 to 1.5 hr, and net fluxes of Ca2+ and H+ were measured in the elongation region. H+ fluxes were much more sensitive to osmotic pressure than were Ca2+ fluxes. Oscillations of 7-min period in H+ flux, normally observed in the control, were almost fully suppressed at high osmotic concentrations. Net H+ flux was shifted from average efflux of 25 +/- 3 nmol m-2 sec-1 to average influx of 10 +/- 5 nmol m-2 sec-1 after the incubation in 100 mm mannitol. The larger the osmotic concentration, the larger was the H+ influx. This flux caused the unbuffered solution of pH 4.85 to change to pH 5.3 after mannitol application. It appears that the osmoticum suppresses oscillatory H+ extrusion at the plasma membrane. Discrete Fourier Transforms of the H+ flux data showed that, apart from suppression of the 7-min oscillations in H+ flux, mannitol also promoted the appearance of faster 2-min oscillations. Ca2+ influx slightly increased after mannitol treatment. In addition the 7-min oscillatory component of Ca2+ flux remained apparent thereby showing independence of H+ flux.
Shabala
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Department of Physics, University of Tasmania, GPO Box 252-21, Hobart, Tasmania 7001, Australia.
Newman
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D001692:Biological Transport / Q000187:drug effects; D002118:Calcium / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007473:Ion Channels / Q000502:physiology; D007700:Kinetics; D008353:Mannitol / Q000494:pharmacology; D009991:Oscillometry; D009994:Osmolar Concentration; D018517:Plant Roots / Q000502:physiology; D003313:Zea mays / Q000502:physiology*
D007473:Ion Channels; D008353:Mannitol; D002118:Calcium