Dual Mechanisms of Ion Uptake in Relation to Vacuolation in Corn Roots

Abstract

Sumnmiiary. Absorption isothernms for chloride and rubidium ionls have been determined through a wide concentration range for nonvacuolate root tips, and for vacuolate subapical sections of corn root. In the range 0 to 0.5 mm, chloride absorption is hlyperbolic with concentration in both tips and proximal sections. At high concentrations. I to 50 milM, a second multiple-hyperbolic isotherm for chloride is noted in vacuolate tissue, while the isotherm for nonvacuolate tips rises exponentially. A linear to exponentially rising isotherm is taken to signify diffusive permeation.

Presence of Two Different Membrane-bound, KCl-stimulated Adenosine Triphosphatase Activities in Maize Roots

“…Each tionated by either Scheme A or Scher clature is described in Figure 1 associated with the plasmalemma (7,9). The vesicles in this (3,8,12,21) and were also found to be charache final equilibrium posi-teristics of the KCI-stimulated ATPase associated with ity gradient is a function plasmalemma-rich fraction from oat roots (12). vesicle and the osmotic On the basis of the similarity between the kinetics of KCIer explanations have also activation of the plasmalemma-associated ATPase activity of oat roots and the kinetics of ion uptake by excised oat roots, tained both plasmalemma it has been speculated (12) that this enzyme might be involved was sought to determine in the transport of ions across the plasmalemma.…”

Multiphasic Absorption of Glucose and 3-O-Methyl Glucose by Aged Potato Slices

“…The core section was pierced with a 10 mm diameter stainless steel tube, and the 10 mm tissue core subsequently was sliced to yield 1 mm thick discs. The discs were aged for 24 hr with gentle rotary shaking (15). The washing solution (0.2 mm CaSO4) was changed eight times over the first 12 hr.…”

Electrostatic Association and Donnan Phenomena as Mechanisms of Ion Accumulation

“…The high-concenitration imiechanislmi contributes negligiblv to ionl utptake froni sollutioins of less than 1 IllM buit at salt concenitrations exceedinig 1 mim, ion uptake is equal to the sum111 of the absorption by both mechanisms. Ion uptake by the lowv-concentration mechanism appears to be indifferent to the nature of the coutnterioni, \hile uptake by the higlh-concentration mnechanisnm is markedly influenced by the counterion (3,6,21).…”