The photochemical activities of chloroplasts isolated from bundle sheath and mesophyll cells of maize (Zea mays var. DS606A) have been measured. Bundle sheath chloroplasts are almost devoid of grana, except in very young leaves, while mesophyli chloroplasts contain grana at all stages of leaf development.Chloroplast fragments isolated from bundle sheath cells showed a light-dependent reduction of potassium ferricyanide, 2,6-dichlorophenolindophenol, mammalian cytochrome c, plastocyanin, and Euglena cytochrome cm. These activities were inhibited by 3-(3,4-dichlorophenyl)-1 , l-dimethylurea at 1.25 micromolar. However, the photoreduction of NADP from water was extremely low or absent, except in chloroplasts from very young leaves, and the capacity for NADP reduction appeared to be related to the degree of grana formation.Photosystem I activity was present in bundle sheath chloroplast preparations at all stages of leaf growth and senescence examined. However, the activity was lower than in isolated mesophyll ehloroplasts. NADPH diaphorase activity was comparable in both types of chloroplast.Chloroplasts appearance of photosystem II activity in developing pea chloroplasts appears to be correlated with the formation of grana, rather than with the production of chlorophyll (5). In leaf sections of plants containing the C4-dicarboxylic acid pathway of photosynthesis, in which both granal and agranal chloroplasts are present, photoreduction of the Hill oxidant, tetranitro blue tetrazolium chloride, was observed only in grana-containing chloroplasts (6, 7). Agranal chloroplasts isolated from the bundle sheath cells of the C4 plants, maize and Sorghum, contain photosystem I activity, but do not photoreduce NADP from water, whereas the granal mesophyll chloroplasts carry out this reaction (2,3,19).Similar correlations between photosystem II activity and the presence of grana have been made in algae. The chloroplasts of the green alga Chlamydobotrys stellata contain appressed lamellae and carry out normal photosynthesis when grown photoautotrophically. However, when the alga was grown photoheterotrophically on acetate, nearly all the chloroplast lamellae were separated from each other and the chloroplasts lacked photosystem II activity (16,17). Both photosystem II activity and appression of lamellae were regained when photoautotrophic growth was resumed, again indicating that appressed lamellae are necessary for photosystem II activity (16)(17)(18).In contrast, photosystem II activity is present in a mutant of C. reinhardi (ac-31) which has chloroplasts that contain only unappressed lamellae (8). Algae belonging to the Rhodophyta and Cyanophyta do not contain appressed lamellae yet evolve oxygen in the light. The disruption of grana by suspension of higher plant chloroplasts in a low salt medium does not result in a loss of photosystem II activity (10). Studies on a mutant of Chlamydomonas reinhardi revealed no correlation with Hill activity and grana formation (13).The occurrence of two morphologically distinct chl...
