Cortical cell fluxes and transport to the stele in excised root segments of Allium cepa L. : IV. Calcium as affected by its external concentration.

摘要: From compartmental analysis of radioisotope elutin measurements, fluxes Ca(2+) were estimated for cortical cells in root segments onion, Allium cepa L., relative to complete nutrient solutions containing a range calcium concentrations ([Ca0]) from 2 μeq l(-1) 20 meq l(-1), increasing 10-fold steps Ca(2+). Except the counter-ion (usually NO 3 (-) , sometimes Cl(-) at highest [Ca0]), composition solution was other-wise same all concentrations. Compartmental indicated that cytoplasm had high content exchangeable but, light evidence animal studies, ionic activity assumed be no greater than 0.002 ml(-1). With Ussing-Teorell flux equation as criterion, it concluded values [Ca0] tested, entered passively and actively pumped back into external solution. Entry vacuole active cases. The conclusions regarding character ion transport across plasmalemma when whole taken contribute activity. However, electrochemical gradient very much steeper formerly estimated. Calcium transported stele proportion moved xylem almost exclusively basipetal direction.