Intercellular Transport in Plants: I. THE RATE OF TRANSPORT OF CHLORIDE AND THE ELECTRIC RESISTANCE

A quantitative study has been made of the intercellular movementof chloride in Chara corallina, using pairs of joined internodalcells. One cell of the pair (cell 1) was exposed to a solutioncontaining ³⁶Cl; the distribution of this tracer between thecells was determined at the end of the uptake period. Of thechloride taken up, 0.29 was transported out of cell 1 for alluptake times from 1.8 to 22 ks and 0.57 was transported to thevacuole of cell 1, in experimental series I. In series II, thefraction transported out of cell 1 was 0.43 at 22 and 43 ks,but 0.17 at 600 s. These results represent a rate of transport of 4 to 60 pmols^–1, across an intercellular wall of area 1.5 x 10^–6m²; the wall has 0.03 to 0.04 of its area occupied by plasmodesmata.The estimate of transport rate is based on an attempt to determinethe specific activity of the cytoplasm of cell 1. The electricresistance of the node was found to be 47 m m². The observed transport rate can be explained by diffusion inthe plasmodesmata, without the need to postulate active processes.Diffusion in the plasmodesmata is slower than in free solutionby an ‘impediment factor’ of 7 to 700, dependingon the assumed chloride concentration of the ground-plasm. Ifthe plasmodesmata offer the major conducting path for electriccurrent, the electric impediment factor is 390. Chloride entersthe plasmodesmata from the same small kinetic compartment whichsupplies the flux to the vacuole, or from a smallintermediatecompartment.