Sulfide‐induced oxygen uptake by isolated spinach chloroplasts catalyzed by photosynthetic electron transport

In addition to an inhibitory effect on the photoreduction of NADP+ by isolated spinach chloroplasts (Spinacea oleracea L. cv. Melody Hybrid), sulfide initiated oxygen uptake by chloroplasts upon illumination, both in presence and absence of an electron acceptor. Sulfide‐induced oxygen uptake was sensitive to DCMU demonstrating the involvement of photosynthetic electron transport. Addition of superoxide dismutase to the chloroplast suspension prevented the sulfide‐induced oxygen uptake, which indicated that sulfide may be oxidized by the chloroplast, its oxidation being initiated by superoxide formed upon illumination (at the reducing side of PSI). Tris‐induced inhibition of NADP+ photo‐reduction could not be abolished by sulfide, which indicated that sulfide could not act as an electron donor for PSI.