Oscillation in Photosystem II Activity of Chloroplasts Isolated from Dark Adapted Wheat Seedlings

Abstract

Endogenous rhythms in photosynthetic light reactions have been demonstrated in many algae and some higher plants under continuous dim light conditions (1–3). in chloroplasts isolated from the ~ primary leaves of wheat seedlings grown in continuous bright (≃20 W m-2) light, we observed an oscillation in photosystem II (PS II) catalyzed 2,6-dichlorophenol indophenol (DCPIP) photoreduction activity with a periodicity of about 12 h (4). Persistent rhythms in photosynthetic O2 evolution and CO2 fixation in bright continuous light have also been reported in Acetabularia (5) and Arachis hypogaea (8), respectively. Although the persistence of photosynthetic rhythms in plants adapted to continuous light (LL) have been well documented, only limited studies have been made on the existence of photosynthetic rhythms in plants adapted to continuous darkness (DD). for instance, expression of rhythms in net photosynthesis has been shown only in Acetabularia (7) and Chenopodium rubrum (8) maintained in continuous darkness.