E. Hilary Evans

A rapid method for extraction of oxygen-evolving photosystem 2 preparations from cyanobacteria

Considerable interest has been generated in the mechanism of action of photosystem 2 of chloroplast and cyanobacterial photosynthesis. One approach in the investigation of this problem has been the isolatioff of preparations retaining activities associated with photosystem 2, in particular that of light-induced reduction of DCPIP using an artificial electron donor to photosystem 2 such as diphenylcarbazide. Such cyanobacterial preparations have been reported, derived from Synecoccus [ 11, Chlorogloea fritschii [2] and Anacystis nidulans [3], which exhibit broadly similar denaturing polyacrylamide gel patterns. However only one method for photosystem 2 preparation which retains oxygen evolving capacity has been reported, using the thermophilic cyanobacterium Phormidium laminosum [4]. Here, we report a more rapid method of preparation of a cyanobacterial membrane fraction retaining oxygen-evolving capacity which we believe may be generally applicable to cyanobacteria, to which the method in [4] is not.

Control of photosynthesis during nitrogen depletion and recovery in a non-nitrogen-fixing cyanobacterium

When cells of Synechocystis strain PCC 6308 are starved for nitrogen, the amount of stored carbohydrate increases, the phycocyanin to chlorophyll a ratio decreases, and the rates of oxygen evolution and of carbon dioxide fixation decrease. When nitrate-nitrogen is replenished, the amount of carbohydrate decreases, the rate of oxygen evolution increases immediately, preceeding the increase in phycocyanin or carbon dioxide fixation. The rate of respiration first increases and then decreases upon nitrogen addition. Nitrogen-starved cells show no variable fluorescence; variable fluorescence recovered in parallel with oxygen evolution. This suggests that photosystem II is inactive in nitrogen depleted cells and not blocked by a build up of metabolic endproducts. Since carbon dioxide fixation does not increase until two to four hours after nitrate is replenished to nitrogen starved cells, it is suggested that reducing power may first be needed within the cell for some other process than photosynthesis, such as nitrate reduction.

Detection of allophycocyanin in photosystem I preparations from the blue--green alga, Chlorogloea fritschii.

Photosystem I particles have been prepared from higher plant and eukaryotic algal chloroplasts and prokaryotic blue-green algae by essentially similar techniques [ 1,2]. Photosynthetic membrane of bluegreen algae have been extracted with sodium dodecyl sulphate [3,4] Triton X-100 [5,6] or digitonin [7] and the resulting extracts purified via ammonium sulphate precipitation and hydroxylapatite chromatog raphy [3,4] or by centrifugation and DEAE-cellulose chromatography [5-71. All these extracts have shown photosystem 1 activity with ratios of P700 : chlorophyll of 1 : 40-45, although some differences in protein composition have been noticed. The composition of blue-green algal photosystem I particles has been considered [l-7] essentially similar to particles derived from higher plant eukaryotic chloroplasts, with respect to pigment composition, only chlorophyll IZ and carotenoids, mainly p-carotene [ 1,4,7] being present. Blue-green algae differ in gross pigment composition from higher plants and eukaryotic algae due to the presence of phycocyanins and the absence of chlorophyll b (see [S]). C-phycocyanin is the major phycocyanin component of C fritschii, with trace amounts of allophycocyanin present [8]. It has been suggested that allophycocyanin is a bridging pigment in energy transfer between phycobilisomes and chlorophyll [9]. The presence of allophycocyanin in photosystem I particles prepared from the blue-green alga Chlorogloea fritschii is reported here, thus suggesting that there may be a difference between the composition

Whole leaf fluorescence as a technique for measurement of tolerance of plants to heavy metals

Heavy metal tolerance is usually measured by root elongation (Witkins 1978) or by the effect of increasing heavy metal concentrations on yield (Davis and Beckett 1978). Both these methods suffer from being relatively slow. It has been suggested that the accumulation of heavy metals in the chloroplast may be critical in determinging tolerance (Ernst et al. 1978). Workers with isolated chloroplasts have concluded that heavy metals inhibit the water splitting reactions of photosystem 2 (Miles et al. 1972; Cedeno-Maldonado et al. 1972; Bazzaz et al. 1974), and Photosystem 1 has also been shown to be affected (Wang et al. 1976). Both Photosystems 1 and 2 may be conveniently assayed by characteristic fluorescence (Gregory 1977), and work by Amdt (1974) has confirmed that the induction kinetics of chloroplast fluorescence is inhibited by copper, manganese and zinc. Here it is proposed that room temperature whole leaf fluorescence measurements may be used as a rapid tolerance assay.

THE INTERACTION OF CHLOROPHYLL-A WITH DETERGENT MICELLES

Absorption and fluorescence spectra of Chl‐a in ethanol, ethanol/water mixtures and aqueous sodium dodecyl sulphate are reported. Contrary to a previous report, it is found that Chl‐a is not solubilized in the anionic detergent as a microcrystalline form.

Time-resolved spectroscopy of photosynthetic systems using synchrotron radiation: II: Photosystem 2 preparations from lettuce

Abstract Fluorescence decay profiles for Photosystem 2 preparations from lettuce are presented. The profiles are complex and require at least three exponential components to explain the data. The observations are discussed in terms of current models for PS2 fluorescence, but it is concluded that none of them is really adequate to explain the data.

Time-resolved spectroscopy of photosynthetic systems. 3: photosystem 1 preparations from the cyanobacterium Chlorogloea fritschii

Abstract Fluorescence decay profiles for a photosystem 1 preparation from the cyanobacterium Chlorogloea fritschii are reported. The decay profiles are dominated by a short-lived decay component of some 20–30 ps, but also exhibit two other components of lifetimes 400–650 ps and 3.0–3.6 ns. Time-resolved spectra of the three components of the decay are reported and are assigned principally to chlorophyll—protein complexes with various degrees of coupling to the reaction centre. The effect of redox potential on photosystem 1 is reported. It is concluded that there is a species in the energy transfer chain intermediate between the main light-harvesting pigments and P 700 .

Relationship between growth conditions, cell morphology and carotenoid composition of the Cyanobacterium Chlorogloeopsis (Chlorogloea) fritschii, and carotenoid compositions of photosystem 1 and photosystem 2 preparations

The cell morphology and carotenoid composition of the Cyanobacterium Clorogloea fritschii are known to depend on growth conditions. The presence of sucrose in the medium resulted in an increase in the amount of the carotenoid glycoside myxoxanthophyll and an increased proportion of aseriate cells. The same carotenoids were present in light and dark-grown cultures, but light was needed for these carotenoids to be fixed into photosynthetic membranes. Photosystem 1 and 2 preparations both contained carotenoids; PS1 was enriched in β-carotene, PS2 in myxoxanthophyll. Both photosystems were depleted in echinenone; the location of this in the cell has not been identified.

The identification of desmethylspheroidenone as a major carotenoid in aerobic cultures of Rhodopseudomonas capsulata

Purple non-sulphur photosynthetic bacteria of the Rhodospirillaceae characteristically contain acyclic carotenoids with tertiary methoxy substituents at C-l. For example, in most Rhodopseudomonas species, including Rps. sphaeroides, Rps. gelatinosa and Rps. capsulata, grown in the light under anaerobic conditions the main carotenoids are spheroidene (l-methoxy-3,4-didehydro-l,2,7’,8’-tetrahydro-

Characterisation of the Photosystem II polypeptides of Anacystis nidulans by trypsin digestion, Tris washing and lead incubation

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