Photosystem II Activity in Agranal Bundle Sheath Chloroplasts from Zea mays

Abstract

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...

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

“…Intact bundle sheath cells were prepared from maize leaves by the method of Woo et al (12), and intact mesophyll cells were prepared by maceration (11) of pea leaves. The bundle sheath cells were not separated from each other but were essentially free of mesophyll cells (1 An analysis of the absorbance changes at 554 nm in the fully expanded portion of a maize leaf after ilumination indicated that, in the leaf, cytochrome f was reduced by photosystem II and oxidized by photosystem I. For instance, the magnitude of the absorbance change at 554 nm with 664-nm light, which is absorbed by both photosystems I and II, was 10% of the change obtained using 705-nm light of equal intensity, which is absorbed predominantly by photosystem I.…”

“…Several of the C4 plants, including maize, Sorghum, and sugar cane, are characterized by chloroplasts which show little evidence of grana development in the cells surrounding the vascular bundle. Chloroplasts isolated from these cells do not photoreduce NADP (1)(2)(3)12), even though they contain demonstrable photosystem I and photosystem II activities (1-3). These and related observations (5) have raised the question of whether in the intact cell the bundle sheath chloroplasts are capable of photosynthetically reducing NADP, as is thought to occur in the grana-containing chloroplasts found in C3 plants and in the mesophyll cells of C4 plants.…”

“…If there is also electron flow in the agranal chloroplasts of bundle sheath cells between photosystem II and cytochrome f, photo-oxidation of the cytochrome should vary depending on whether the light given is absorbed by photosystems I and II (<700 nm) or by photosystem I only (>700 nm). The photo-oxidation of cytochrome f in isolated bundle sheath chloroplasts of maize and Sorghum is independent of wavelength (1,12), but chloroplasts in intact bundle sheath cells have not been examined.…”

“…Several of the C4 plants, including maize, Sorghum, and sugar cane, are characterized by chloroplasts which show little evidence of grana development in the cells surrounding the vascular bundle. Chloroplasts isolated from these cells do not photoreduce NADP (1)(2)(3)12), even though they contain demonstrable photosystem I and photosystem II activities (1)(2)(3) important implications to the elucidation of the pathway of carbon in C4 plants and has been the subject of much recent debate (7).…”

pH Dependence and Cofactor Requirements of Photochemical Reactions in Maize Chloroplasts

“…The agranal bundle sheath chloroplasts of maize and Sorghum have been reported to be greatly deficient in photosystem II activity and noncyclic photophosphorylation when compared to the granal mesophyll chloroplasts (2,3,7,8,14,18) and unable to carry out the photoreduction of NADP from water (18). However, significant levels of photosystem II activity have been detected in the bundle sheath chloroplasts of these plants (1,5), and the ability of isolated bundle sheath (10) and ferredoxin NADP-reductase was isolated from the same source by the methods of Borchert and Wessels (6) and Forti and Sturani (9).…”