Euglena gracilis: Phenotypic resistance to 2,4-dinitrophenol

Euglena gracilis, when grown on a medium containing 10^?5m 2,4-dinitrophenol, will initially bleach, cease to divide, and about one-half will die off. After a prolonged lag period of 6–8 days, the remaining cells green and begin to multiply. The resultant cells are resistant to dinitrophenol and will grow in its presence at rates close to those in normal medium. The resistant cells do not differ greatly from the nonresistant ones, except that they show no sign of respiratory control, their photosynthetic activity is somewhat reduced, and their size is larger. The resistant cells appear less motile, their flagellar movement is slower, and their motility appears disturbed (they tend to swim in circles). The resistance is lost when the cells are grown for 2–3 generations on medium lacking dinitrophenol.