Exit of Dye from Nitella with Different Initial Concentrations of Dye in the Vacuole.

Abstract

Living cells of Nitella were placed in brilliant cresyl blue solution for different lengths of time, so that the concentration of dye 1 (DB plus DS) in the vacuole varied from 0.000035 M to 0.0028 M (cell wall only very slightly stained). When such cells were placed in the M/150 phosphate buffer solution at pH 5.4 (solution changed and stirred), the rate of exit of dye from the vacuole was found to be about the same between 0.000035 M and 0.00014 M. Above the latter concentration it decreased as the concentration increased. There is also a decrease in the velocity constant, k, calculated from the equation dx/dt = k(a−x), where a equals the initial concentration of dye in the vacuole, and × equals the amount of dye that has disappeared from the vacuole at time t. The pH value of the sap was about the same as that of the normal (determined after the dye has come out of the vacuole).

It may be assumed that the conditions, either in the vacuole or in the protoplasm or both, change as the concentration of dye increases. This change may be due to the production of a substance which (1) combines with part of DB to form a non-penetrating compound (other than DS), of the same color as DB and DS, which breaks down slowly to form DB during the exit of the dye, or (2) otherwise changes the concentration of DB.