Ion Transport in Nitellopsis Obtusa

Abstract

The distribution and rates of exchange of the ions sodium, potassium, and chloride in single internodal cells of the ecorticate characean, Nitdlopsis obtusa, have been studied.In tracer experiments three kinetic compartments were found, the outermost "free space" of the cell, a compartment we have called "protoplasmic non4ree space", and the cell sap.The concentrations in the vacuole were 54 m~ Na +, 113 mM K +, and 206 m~ C1-. The steady state fluxes across the vacuolar membrane were 0.4 pmole Na+/cm. ~ sec., 0.25 pmole K+/cm. s sec., and 0.5 pmole C1-/cm? sec.The protoplasmic Na/K ratio is equal to that in the vacuole but protoplasmic chloride is relatively much lower. Osmotic considerations suggest a layer 4 to 6 # thick with sodium and potassium concentrations close to those in the vacuole. The fluxes between protoplasm and external solution were of the order of 8 pmoles Na+/ cm. ~ sec. and 4 pmoles K+/cm. 2 sec.We suggest that the protoplasm is separated from the cell wall by an outer protoplasmic membrane at which an outward sodium transport maintains the high K/Na ratio of the cell interior, and from the vacuole by the tonoplast at which an inward chloride transport maintains the high vacuolar chloride. The tonoplast appears to be the site of the principal diffusion resistance of the cell, but the outer protoplasmic membrane probably of the main part of the potential. I N T R O D U C T I O NThere are practically no studies on the ion permeability of plant ceils and tissues which are comparable--in the details elucidated--with those made by animal physiologists on nerve, muscle, and erythrocytes. The plant cell with its cell wall, large central vacuole, and thin layer of protoplasm is sufficiently complicated to make such a study difficult but in the plant physiologists' favourite material--roots, storage tissue, etc.--these difficulties are added to by morphological complications. It has thus been possible less often in plant systems to express the results of an experiment in fully quantitative terms--as an ion flux in pmoles (10 -12 moles) per sq. cm. per second across a well defined morphological boundary separating two phases in which the electrochemical activities of the ion are known. This is the general aim of our work. 335

Active and Passive Transport of Potassium in Cells of Excised Pea Epicotyls

“…The experimental values for each compartment are given in Table I. In general, the results shown in Figures 1 to 3 and Table I agree with similar wash-out data on other plants (10,11) and are consistent with the concept that ions traverse compartments in the series: wall, cytoplasm, and vacuole. The rate constants for loss from each of these compartments show sharp differences from (apparent content X fractional equilibration divided by the uptake (Table II) are reasonably close to those found previously for red beet root tissue (11) and for barley roots (12).…”

“…Alternatively, the cytoplasm and vacuole may each be accessible directly to the free space, in a parallel arrangement. The serial model is the one generally accepted for giant algal cells (2,9,10), and that this model is relevant to higher plant cells has been demonstrated convincingly by Pitman (11) with beet root tissue and Cram (1) with carrot root tissue. It is the serial model, therefore, which we have adopted as the basis for the interpretation of the present data.…”

“…The tubes were Figure 1. This can be considered as a compound curve, made up of first order rate losses from each of several compartments in the tissue; it is amenable to the method of analysis used by others (1,2,(9)(10)(11). This yields a series of straight lines (from semilogarithmic plots) each characteristic of a particular phase.…”

Sodium and Potassium Transport in the Marine Alga Chaetomorpha Darwinii

“…Fluxes of potassium and sodium across the plasmalemma and tonoplast were estimated by a method basically the same as that used by MacRobbie and Dainty (1958) and by Pitman (1963). Strands of Chaetomorpha about 3 cm long (7-10 cells) were put into labelled sea water and after 12 hr transferred to non-radioactive samples of sea water.…”

Compartmentation of Organic Acids in Corn Roots II. The Cytoplasmic Pool of Malic Acid

“…(3) indlicate that this miiem(brane constitutes a very firn barrier, anid the contents of the vacuole are lost to the cytoplasimi at a vrery slow rate, at least in cells of Nitcllopsis obtitsa (11). It therefore seems unlikely that the rapid utilization of the malate produced by CO.) fixation which was brought about by the inhibitors inivolved a mass transfer of material from the vacuole.…”