Photoreduction sites for 2,6-dichlorophenolindophenol in chloroplasts.

2,6-Diclhloroplleniolinidoplheol (D LP1P) is one of tlle mainy comnmloiinly) used electroni acceptors for the light-induced reactions in chloroplasts (2). Until recently, it has generally been assumed that it accepts electrons from the short-wavelengtlh pigment system 2 (PS2). Since the finding that indophenol reduction can be coupled with phlotophosphorylation [see review by Vernon and Avron (8)], the possibility olf its re(luction by the long-wavelength pigment systemii 1 ( PSI) has also been suggested. Recently Kok et al. (5) reported a fast photoreduction of DPI P in clhloroplasts by using pulse illumination. The fast redulction was completely absent in the' Sc'encdcsmt s mutait No. 8 which lacks the long-wavelength reaction center P70(). This note shows that bNy means of senisitive difference spectrophotomletry, photoreduction of DPIP at sites belonging to the 2 pignment systems in chloroplasts canl readily be demloilstrated.