Effect of dibromothymoquinone (DBMIB) on reduction rates of Photosystem I donors in intact chloroplasts.

Dual effect of dibromothymoquinone ( DBMIB ), inhibitor and reducing agent at the donor side of Photosystem I, was investigated in isolated intact chloroplasts by flash-induced absorbance changes at 820 and 515 nm. We show that in the absence of other electron donors, rereduction of P700+ by DBMIB proceeds at a very low rate (half-time of approximately 10 s) Dual effect of DBMIB explains that the initial rise of electrochromic absorbance change induced by repetitive flashes is usually not diminished while the slow rise is fully inhibited by this compound.