Nicotinamide adenine dinucleotide phosphate photoreduction from water by agranal chloroplasts isolated from bundle sheath cells of maize

Abstract

Photoreduction of NADP from water in agranal chloroplasts isolated from the leaf bundle sheath cells of Zea mays (var. DS 606A) or Sorghum bicolor (var. Texas 610) was dependent upon addition of plastocyanin as well as ferredoxin. Activity was further increased by the addition of ferredoxin NADP-reductase. Saturation for plastocyanin was reached at about 6 micromolar. In contrast, grana-containing chloroplasts isolated from leaf mesophyll cells of these plants or from pea (Pisum sativum L.) leaves did not require either plastocyanin or ferredoxin NADP-reductase for NADP photoreduction from water, although with some preparations plastocyanin stimulated the activity.Photosystem I activity, which was low in washed preparations of bundle sheath chloroplasts, was also stimulated by plastocyanin. The effect of plastocyanin on photosystem I activity in the grana-containing chloroplasts was similar to that on NADP photoreduction from water.In the presence of plastocyanin, the rates of NADP photoreduction from water were about the same in the agranal and granal chloroplasts, but photosystem I activity was considerably higher in bundle sheath chloroplasts. In these chloroplasts photosystem II appeared to limit the rate of NADP photoreduction.The results indicated that the agranal bundle sheath chloroplasts reduced plastocyanin via photosystem II and oxidized it via photosystem I. Both types of maize chloroplast photoreduced oxidized plastocyanin, but in the presence of methyl viologen, reduced plastocyanin was photo-oxidized only by the bundle sheath chloroplasts.