Relation of Absorption Coefficients to Rate of Penetration of Dye into the Cell

Abstract

Crystal violet penetrates slowly into the vacuolar sap of Nitella. Is this connected with the presence of 0.1 M KCl in the sap? To what extent can such an effect be interpreted by the multiple absorption coefficient theory? This theory deals only with rates and steady states (not with equilibrium); its basic principle is as follows: Other things being equal the rate of penetration of dye into the sap is a function of the concentration gradient (D'_o—D'_s) of the dye in the plasma membrane: D'_o and D'_s represent the concentrations of dye in the plasma membrane at the outer and inner phase boundaries, and are functions of the absorption coefficient∗ of the dye between the plasma membrane and the aqueous solution at the outer and inner phase boundaries. The rate is also a function of the diffusion coefficient of the dye in the plasma membrane.

The following experiments were made to test these conceptions. Employing a cell model 1 consisting of chloroform (representing the plasma membrane) placed between crystal violet (0.04%) at pH 5.5 and artificial sap at pH 5.5 (representing the vacuolar sap) the passage of dye through the chloroform into the sap during one hour was determined colorimetrically. Absorption coefficients were determined by shaking chloroform with the dye solution or with the sap; these are, C_o = cone, of dye in chloroform/cone, of dye in external dye solution, and C_s = cone, of dye in chloroform/cone. of dye in sap.

Results. (1) When C_o = C_s = 6, with no KC1 in the dye solution or in sap, the rate of penetration of dye into the chloroform and from chloroform into the sap is relatively rapid. The rate is doubled when the concentration of dye in the dye solution is doubled.