The Tetrazolium Reaction as a Measure of the Action of Diquat in Elodea

The production of red triphenyl formazan (hereinafter referred to as TPF) from colorless 2,3,5-triphenyl tetrazolium chloride (hereinafter referred to as TTC) by living cells was used as a vitality indicator for examining the effects of 6,7-dihydrodipyrido[1,2-a:2′,1′-c] pyrazidiinium salt (diquat) in elodea (Elodea canadensisMichx) shoots at varying light intensities. Diquat at 10 ppmw completely killed the elodea in 6 hr at 183 ft-c and at almost the same rate at 13,000 ft-c due to light saturation near the lower level. Over 24 hr were required for this effect in the dark. Between 29 and 183 ft-c, TPF production varied inversely with the light intensity. A comparison is made with the destruction of chlorophyll by diquat.