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.