Biomedical subjects

K S Andersen

Publications and source records attributed to K S Andersen.

52 records · Page 3Linked to original sources

PubMed1972

Photosystem II Activity in Agranal Bundle Sheath Chloroplasts from Zea mays.

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 mesophyll 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 c(552). These activities were inhibited by 3-(3, 4-dichlorophenyl)-1, 1-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 chloroplasts. NADPH diaphorase activity was comparable in both types of chloroplast.Chloroplasts isolated from bundle sheath cells of plants grown under a variety of conditions, including continuous and intermittent light, high and low light intensities, and high temperature, exhibited photosystem II activity.

Journal Article↗

PubMed1972

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

The photo-oxidation of cytochrome f (cytochrome c(554)) in bundle sheath cells isolated from leaves of maize (Zea mays var. DS 606A) has been compared with that in intact maize leaf and in isolated pea leaf cells (Pisum sativum L.). In all cases, illumination with red light caused a negative absorbance change at 554 nm which was attributed to the oxidation of cytochrome f. The extent of this change was greater using monochromatic red light at wavelengths above 700 nm compared with wavelengths below 700 nm. 3-(3,4-Dichlorophenyl)-1, 1-dimethylurea abolished this difference in bundle sheath cells. After illumination for 1 minute or longer in bundle sheath cells, reduction of cytochrome f in the dark was rapid only if the wavelength of the illuminating light was below 700 nm. In the presence of 3-(3,4-dichlorophenyl)-1, 1-dimethlyurea, reduction was slow after illumination at all wavelengths.Cytochrome f photo-oxidation was also followed in cells of a mutant of Chlamydomonas reinhardi, ac-21, which has isolated chloroplasts that exhibit photochemical reactions similar to those shown by isolated bundle sheath chloroplasts. No evidence was obtained for photoreduction of cytochrome f in the mutant.It was concluded that in the chloroplast of the intact bundle sheath cell of maize there is electron flow between photosystem II and cytochrome f resulting in photoreduction of the cytochrome.

Journal Article↗

PubMed1972

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

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.

Journal Article↗

PubMed1972

pH Dependence and Cofactor Requirements of Photochemical Reactions in Maize Chloroplasts.

The pH dependence of the photoreduction of ferricyanide and the photoreduction of NADP from water and photosystem I activity have been compared in isolated chloroplasts from mesophyll and bundle sheath cells of Zea mays. The maximum activity of photoreduction of ferricyanide occurs at pH 8.5 in isolated mesophyll chloroplasts. The addition of methylamine does not cause a marked shift in the pH maximum, but brief sonication lowers the pH maximum to 7.0. In contrast, isolated bundle sheath chloroplasts have a pH maximum at 7.0 and the shape of the pH versus activity curve is similar to that of sonicated mesophyll chloroplasts. When photoreduction of ferricyanide by the isolated chloroplasts is measured at their pH maxima, the values for bundle sheath chloroplasts are about half those of methylamine-treated mesophyll chloroplasts on a chlorophyll basis.The pH maxima for the photoreduction of NADP from water and photosystem I activity are similar in both mesophyll and bundle sheath chloroplasts with maximum activity occurring at pH 7.0 in both cases. In the presence of added plastocyanin and ferredoxin NADP-reductase, the photosystem I activities of both sonicated mesophyll and sonicated bundle sheath chloroplasts are significantly higher than those of the unsonicated preparations. On a chlorophyll basis, photosystem I activity of bundle sheath chloroplasts is at least twice that of mesophyll chloroplasts.

Journal Article↗

PubMed1972