English: The site-specific P-ETC inhibitors were added to Lyngbya (A) or Nostoc (B) at 2 hours intervals at the following cumulatively increasing concentrations: 1, 5, 10, 25, 50, 75 and 100 µM for DCMU (thin black lines), DBMIB (thick gray lines) and PMA (thick black lines); or 5, 10, 25, 50, 100, 150 and 200 µM for CCCP (thin gray lines) as indicated by arrows. The electrogenic activity was monitored under constant illumination and at 1 KΩ fixed external resistance. The effect of DBMIB on electrogenic activity of Nostoc is shown in the inset. The experiments were repeated three times giving consistent results. (C) Schematic diagram showing P-ETC and sites targeted by inhibitors. Cyclic electron transfer (Q-cycle) is indicated by dashed line.