Photoreduction of quinones by isolated spinach chloroplasts

Photoreducibility by isolated spinach chloroplasts of 1,4-benzoquinone, tetrachloro-p-benzoquinone, 2,3-dichloro; 2-chloro-3-amino; 2-methyl, and non-substituted 1,4-naphthoquinones were studied together with oxygen evolution by the Hill reaction. It has been observed by a spectrophotometric method that the naphthoquinones were quantitatively photoreduced to corresponding hydroquinones under anaerobic conditions and readily reoxidized to the original naphthoquinones by molecular oxygen. The naphthoquinones showed no oxygen evolution by the Hill reaction. On the other hand, tetrachloro-p-benzoquinone and p-benzoquinone were photoreduced to hydroquinone under aerobic and anaerobic conditions, and stoichiometric oxygen evolution was observed by the Hill reaction. A possible correlation between the photoreducibility of these quinones and their phytotoxicity was discussed.