An acridine probe into the physiological state of the cell.

Acridine orange was used as a probe to look into the physiological state of the yeast cell, particularly as regards the change in the properties of the membrane (which acts as a barrier against the incoming acridine orange) and the availability of binding sites for acridine orange in chromosomal DNA during growth. After acridine orange had been introduced into the cell, the genetic change at a specific locus with incubation time was measured photodynamically. A three-fold increase in the rate of penetration of acridine orange into the cell was observed, for instance, in going from the resting phase to the dividing phase. A five-fold increase was observed in the number of binding sites in chromosomal DNA under the same transition of the cell. These two parameters may be useful as a measure of the physiological changes in the cell. Some environmental factors such as pH and temperature were also demonstrated to affect the parameters.