Nicotinamide Adenine Dinucleotide Phosphate Photoreduction from Water by Agranal Chloroplasts Isolated from Bundle Sheath Cells of Maize

Abstract

P'hotoreduction 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 NADPreductase. 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 sativuin 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 plastoeyanin. 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 photosvstem 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.The agranal chloroplasts found in the bundle sheath cells of certain plants, including maize and Sorghum, when isolated from the cells do not have the capacity to photoreduce NADP (1, 4, 5,25). In contrast the isolated grana-containing chloroplasts of the mesophyll cells of the same plants carry out a normal photoreduction of NADP. This difference between the two chloroplast types has been attributed to a deficiency of photosystem 11 (25) In this paper we show that maize bundle sheath chloroplasts will photoreduce NADP from water when supplemented with the copper-containing electron transfer protein plastocyanin, ferredoxin, and ferredoxin NADP-reductase.A preliminary account of some of the results in this paper has been published (20). MATERIALS AND METHODSThe growth of maize plants (Zea mays var. DS 606A) in a greenhouse, the isolation of mesophyll chloroplasts and bundle sheath chloroplast fragments, and the assay of chlorophyll and photochemical activities were as previously described (1), except that the volume of assay mixtures was 0.75 ml. Sorghum bicolor var. Texas 610 was treated similarly. The ratio of chlorophyll a to chlorophyll b in isolated bundle sheath chloroplasts was about 6.0. Chloroplasts were isolated from the leaves of Pisum sativum L. by following the procedure used for maize mesophyll chloroplasts.Plastocyanin was isolated from leaves of silver beet (Beta vulgaris) following the procedure of Katoh et al. (15). The concentration...

Photoreduction and Oxidation of Cytochrome f in Bundle Sheath Cells of Maize

“…There is a definite effect of wavelengths below 700 nm on cytochrome f oxidation compared with wavelengths above 700 nm. The changes observed are similar to those obtained with a suspension of pea leaf cells prepared by a technique designed to release mesophyll cells from dicotyledonous leaves (1 1 (10).…”

Photoassimilation of CO2 by Isolated Bundle‐Sheath Strands of Zea mays I. Stimulation of CO2 Assimilation by Adding Various Intermediates of the Photosynthetic Cycle; Evidence for a Deficient Photosystem II Activity

“…The application of this scheme to species possessing agranal cMoroplasts in BS cells presents difiBculties due to the existetice of a low reducing capacity in those chloropiasts. In particular, photosystem n activities appear to be much lower in BS than in mesophyll chloropiasts (Anderson et al, 1971) although there is disagreement on this point (Smillie et at, 1972). Also, the agranal chloropiasts of tnaize are not able to reduce NADP in the absence of added compounds such as plastocyanin, ferredoxixi and ferredoxin-NADP reductase (Smillie et at, 1972).…”

Development of photoreductive activity in plastids of a virescens mutant of barley

“…The three types of photoreductive activities shown in Fig. 2 were until recently thought to measure (A) electron flow through both photosystems I and I1 when NADP was photoreduced with water as electron donor (3,14); (B) electron flow through photosystem I when NADP was photoreduced with ascorbate and DCIP as electron donor in the presence of DCMU (3,14); and (C) electron flow through photosystem I1 when reduction of ferricyanide was measured (3).…”