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

Abstract

The photo-oxidation of cytochrome f (cytochrome c,54) 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 /. 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 , l-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.The chloroplasts of plants possessing the Hatch-Slack or C4 pathway of photosynthesis (C4 plants) often show distinct differences in structure, composition, and photosynthetic activities compared to chloroplasts from plants containing the Calvin cycle (C3 plants) (7). 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. The answer to this question has 'Visiting scientist from Institute of Genetics, Copenhagen University, 0ster Farimagsgade 2A, DK1353, Denmark.

Changes in the Reactivity of the Photosynthetic Apparatus in Heterotrophic Ageing Cultures of Scenedesmus obliquus

“…However, only an increased oxidation level was observed in cells illuminated with either 701 nm light or treated with DCMU and illuminated with any one of the three selected wavelengths. These experiments and those with autotrophic ceils of Scenedesmus are in good agreement with those reported earlier (Bishop et al 1972).…”

“…Since Cyt/is oxidized by photosystem I and reduced by photosystem II its redox kinetics will provide more information about the potency of the two photosystems. Bishop et al (1972), reported for isolated leaf cells that light above 700 nm, activating mainly photosystem 1, caused a very rapid and complete oxidation of Cyt / Since photosystem II could not produce sufficient reductants under these conditions, the dark reversal of the oxidized Cyt/was slowed down. On the other hand, wavelengths below 700 nm cause a comparatively lower oxidation level of Cyt / but produce more reductants for its dark reversal.…”

Photosystem II Activity in Agranal Bundle Sheath Chloroplasts from Zea mays

“…The independence of the photo-oxidation of cytochrome f from wavelength shown by bundle sheath chloroplast preparations has been interpreted as evidence of the inactivity of photosystem 11 (19), but could also be due to reductants produced in photosystem II being unavailable to photosystem I. The question of whether photosystems I and II are linked for electron flow in intact bundle sheath cells is considered in an accompanying paper (4).…”

Organization and activity of photosystems in the mesophyll and bundle sheath chloroplasts of maize

“…PSII activity did not disappear indicating that loss of the ability to photoreduce NADP + was due to unlinking of the photosystems. Bishop et al (1972) also suggest that in BS chloroplasts of maize, PSII is not disappearing but rather that two photosystems are becoming disconnected. No Hill reaction activity in BS chloroplasts of maize was also found by Ku et al (1974) with ferricyanide or DCPIP as the Hill oxidant.…”