Degradation of proteins from thylakoid membranes in senescing wheat leaves at high temperature

This investigation determined whether thylakoid proteins would be degraded more rapidly or not in senescing wheat (Triticum aestivum L. em. Thell.) leaves concurrently exposed to high temperatures. Excised leaves were pulse-labelled with [³⁵S]-methionine for a 12 h period, and then incubated at 22,32 or 42°C for 0, 1, 2, or 3 d, before extracting a thylakoid enriched membrane sample. After electrophoretic separation, two prominent [³⁵S]-labelled protein bands were chosen for further analyses. Band A contained the D-1 thylakoid protein and band B contained thylakoid proteins of the light harvesting complex (LHCII) associated with photosystem II (PSII). Total protein, [³⁵S]-labelled protein, band A protein, and band B protein within the thylakoid enriched membrane samples were measured. Unlabelled thylakoid enriched membrane samples, extracted from leaves given similar treatments, were used to measure uncoupled whole-chain and photosystem II (PSII) electron transport and chlorophyll fluorescence. Accentuated decline in whole-chain and PSII electron transport, increasing F_o values, and decreasing F_max values were a result of high temperature injury in leaves treated at 42°C. None of the thylakoid enriched membrane protein fractions were degraded more rapidly in high-temperature treated leaves. Degradation of the total [³⁵S]-labelled membrane proteins and band B was inhibited by the 42°C treatment. The results indicate that high temperature stress may disrupt some aspects of normal senescence.     

The structure and function of the chloroplast photosynthetic membrane — a model for the domain organization

Recent work on the domain organization of the thylakoid is reviewed and a model for the thylakoid of higher plants is presented. According to this model the thylakoid membrane is divided into three main domains: the stroma lamellae, the grana margins and the grana core (partitions). These have different biochemical compositions and have specialized functions. Linear electron transport occurs in the grana while cyclic electron transport is restricted to the stroma lamellae. This model is based on the following results and considerations. (1) There is no good candidate for a long-range mobile redox carrier between PS II in the grana and PS I in the stroma lamellae. The lateral diffusion of plastoquinone and plastocyanin is severely restricted by macromolecular crowding in the membrane and the lumen respectively. (2) There is an excess of 14±18% chlorophyll associated with PS I over that of PS II. This excess is assumed to be localized in the stroma lamellae where PS I drives cyclic electron transport. (3) For several plant species, the stroma lamellae account for 20±3% of the thylakoid membrane and the grana (including the appressed regions, margins and end membranes) for the remaining 80%. The amount of stroma lamellae (20%) corresponds to the excess (14–18%) of chlorophyll associated with PS I. (4) The model predicts a quantum requirement of about 10 quanta per oxygen molecule evolved, which is in good agreement with experimentally observed values. (5) There are at least two pools of each of the following components: PS I, PS II, cytochrome bf complex, plastocyanin, ATP synthase and plastoquinone. One pool is in the grana and the other in the stroma compartments. So far, it has been demonstrated that the PS I, PS II and cytochrome bf complexes each differ in their respective pools.Abbreviations PS I and PS II Photosystem I and II - P 700 reaction center of PS I - LHC II light-harvesting complex II     

Photosynthetic control, “energy-dependent” quenching of chlorophyll fluorescence and photophosphorylation under influence of tertiary amines

The effects of the tertiary amines tetracaine, brucine and dibucaine on photophosphorylation and control of photosynthetic electron transport in isolated chloroplasts of Spinacia oleracea were investigated. Tertiary amines inhibited photophosphorylation while the related electron transport decreased to the rates, observed under non-phosphorylating conditions. Light induced quenching of 9-aminoacridine fluorescence and uptake of ¹⁴C-labelled methylamine in the thylakoid lumen declined in parallel with photophosphorylation, indicating a decline of the transthylakoid proton gradient. In the presence of ionophoric uncouplers such as nigericin, no effect of tertiary amines on electron transport was seen in a range of concentration where photophosphorylation was inhibited. Under the influence of the tertiary amines tested, pH-dependent feed-back control of photosystem II, as indicated by energy-dependent quenching of chlorophyll fluorescence, was unaffected or even increased in a range of concentration where 9-aminoacridine fluorescence quenching and photophosphorylation were inhibited. The data are discussed with respect to a possible involvement of localized proton flow pathways in energy coupling and feed-back control of electron transport.Abbreviations 9-AA 9-aminoacridine - J _e flux of photosynthetic electron transport - PC photosynthetic control - pH₁ H⁺ concentration in the thylakoid lumen - pmf proton motive force - _P potential quantum yield of photochemistry of photosystem II (with open reaction centers) - Q _A primary quinone-type electron acceptor of photosystem II - q _Q photochemical quenching of chlorophyll fluorescence - q _E energy-dependent quenching of chlorophyll fluorescence - q _AA light-induced quenching of 9-amino-acridine fluorescence     

New approach of monitoring changes in chlorophyll a fluorescence of single guard cells and protoplasts in response to physiological stimuli

A new type of microfluorometer was applied to assess photosynthesis at the single-cell level by chlorophyll fluorescence using the saturation pulse method. A microscopy–pulse amplitude modulation (PAM) chlorophyll fluorometer was combined with a Zeiss Axiovert 25 inverted epifluorescence microscope for high-resolution measurements on single mesophyll and guard cells and the respective protoplasts. Available information includes effective quantum yield of photosystem II, relative electron transport rate and energization of the thylakoid membrane due to the transthylakoidal proton gradient. Dark–light induction curves of guard cell (GCPs) and mesophyll cell protoplasts (MCPs) displayed very similar characteristics, indicating similar functional organization of thylakoid membranes in both types of chloroplasts. Light response curves, however, revealed much earlier saturation of photosynthetic electron flow in GCPs than in MCPs. Under anaerobiosis, photosynthetic electron flow and membrane energization were severely suppressed. A similar effect was observed in guard cells when epidermal peels were incubated with the fungal toxin fusicoccin which activates the plasma membrane H⁺-ATPase and causes irreversible opening of stomata. The drop in electron transport rate was prevented by blocking ATP consumption of the H⁺ pump or by glucose addition. These results show that chlorophyll fluorescence quenching analysis allows profound insights into stomatal physiology.     

Biotic stress induced demolition of thylakoid structure and loss in photoelectron transport of chloroplasts in papaya leaves.

Papaya mosaic virus (PMV) causes severe mosaic symptoms in the papaya (Carica papaya L.) leaves. The PMV-induced alterations in photosystem II (PS II) structure and photochemical functions were probed. An increase in chlorophyll a (Chl a) fluorescence polarization suggests pathogen-induced transformation of thylakoid membrane to a gel phase. This transformation in physical state of thylakoid membrane may result in alteration in topology of pigments on pigment-binding proteins as reflected in pathogen-induced loss in the efficiency of energy transfer from carotenoids to chlorophylls. The fast Chl a fluorescence induction kinetics of healthy and PMV-infected plants by F(O)-F(J)-F(I)-F(P) transients revealed pathogen-induced perturbation on PS II acceptor side electron transfer equilibrium between Q(A) and Q(B) and in the pool size of electron transport acceptors. Pathogen-induced loss in photosynthetic pigments, changes in thylakoid structure and decrease in the ratio of F(V)/F(M) (photochemical potential of PS II) further correlate with the loss in photoelectron transport of PS II as probed by 2,6-dichlorophenol indophenol (DCPIP)-Hill reaction. Restoration of the loss by 1,5-diphenyl carbazide (DPC), an exogenous electron donor, that donates electron directly to reaction centre II bypassing the oxygen evolving system (OES), leads towards the conclusion that OES is one of the major targets of biotic stress. Further, the data suggest that chlorophyll fluorescence could be used as a non-invasive handy tool to assess the loss in photosynthetic efficiency and symptom severity in infected green tissues vis-a-vis the healthy ones.     

Differential detergent-solubilization of integral thylakoid membrane complexes in spinach chloroplasts. Localization of photosystem II, cytochrome b6-f complex and photosystem I

Progressive solubilization of spinach chloroplast thylakoids by Triton X-100 was employed to investigate the domain organization of the electron transport complexes in the thylakoid membrane. Triton/chlorophyll ratios of 1:1 were sufficient to disrupt fully the continuity of the thylakoid membrane network, but not sufficient to solubilize either photosystem I (PSI), photosystem II (PSII) or the cytochrome b6-f(Cyt b6-f) complex. Progressive with the Triton concentration increase (Triton/Chl greater than 1:1), a differential solubilization of the three electron transport complexes was observed. Solubilization of the Cyt b6-f complex from the thylakoid membrane preceded that of PSI and apparently occurred early in the solubilization of stroma-exposed segments of the chloroplast lamellae. The initial removal of chlorophyll (up to 40% of the total) occurred upon solubilization of PSI from the stroma-exposed lamella regions in which PSI is localized. The tightly appressed membrane of the grana partition regions was markedly resistant to solubilization by Triton X-100. Thus, solubilization of PSII from this membrane region was initiated only after all Cyt b6-f and PSI complexes were removed from the chloroplast lamellae. The results support the notion of extreme lateral heterogeneity in the organization of the electron transport complexes in higher plant chloroplasts and suggest a Cyt b6-f localization in the membrane of the narrow fret regions which serve as a continuum between the grana and stroma lamellae.     

High-temperature damage and acclimation of the photosynthetic apparatus

The influence of mono- (K⁺) and divalent (Mg²⁺) cations and protons (pH) on the temperature sensitivity of thylakoid membranes was investigated in three groups of young bean plants (control, heat-acclimated and non-acclimated). Thylakoid-membrane function was monitored by second and millisecond delayed fluorescence and 9-aminoacridine fluorescence quenching. It was established that metal ions at investigated concentrations decreased the thermostability of the photosynthetic parameters — an increase of MgSO₄ concentration from 0.1 to 20 mM decreased the temperature of their half-inactivation (T50) by 13°C. At the same time the pH dependence of the thermal stability of these parameters showed a maximum at pH 5.5–6.5. The half-inactivation temperatures of those photosynthetic parameters connected with the ability of the thylakoid membrane to form light-induced proton gradients increased by 6–7°C in the heat-acclimated plants compared with the control. It was assumed that the temperature inactivation of photosynthetic electron transfer and the energization of the thylakoid membrane was determined both by the thermoinduced dissociation of the light-harvesting chlorophyll a/b protein complex from PSII, leading to destruction of the excitation energy transfer to the reaction centres, and by the thermal denaturation of the membrane-protein components. The rate of these processes was probably controlled by the size of the negative surface charge and the viscosity of the thylakoid membrane.Abbreviations 9-AA 9-aminoacridine - DF delayed fluorescence - LHCP light-harvesting chlorophyll a/b protein complex - PSI (II) photosystem I (II) - T50 temperature of 50% inhibition of photosynthetic parameter - Tricine N-[2-hydroxy-1, 1-bis(hydroxymethyl)ethyl] glycine     

Changes in Chlorophyll Content and Organization During Senescence of the Primary Leaves of Phaseolus vulgaris L. in Relation to Photosynthetic Electron Transport

A large decrease was observed in the chlorophyll content ofthe primary leaves of Phaseolus vulgaris during senescence.Chloroplasts isolated from mature and senescent leaves gavevery similar light saturation curves for electron transportreactions involving either PS I or PS II, indicating that theaverage number of chlorophyll molecules associated with eachreaction centre did not change during senescence. It is concludedthat the reaction centres ceased to function at the same timeas, or perhaps before, their antenna chlorophylls were lostfrom the thylakoid membrane, and that the percentage decreasein the number of functional reaction centres per leaf was atleast as great as the percentage decrease in the leaf chlorophyllcontent. The chlorophyll-protein composition of thylakoid membrane preparationswas examined by electrophoresis of samples treated with sodiumdodecyl sulphate. In older leaves a smaller proportion of thechlorophyll applied to polyacrylamide gels was associated withthe P700- chlorophyll a-protein complex. There was also a declinein emission at 734 nm in the 77 °K fluorescence spectrumof intact leaf tissue during senescence. These results indicatethat older leaves contained a smaller proportion of chlorophyllsassociated with PS I, and this is consistent with the decreaseobserved in the leaf chlorophyll a/b ratio during senescence.The effect of these changes in chlorophyll content on the capacityof the chloroplast to carry out photosynthetic electron transportis discussed.     

Protein-specific energy requirements for protein transport across or into thylakoid membranes. Two lumenal proteins are transported in the absence of ATP.

Cytosolically synthesized thylakoid proteins must be translocated across the chloroplast envelope membranes, traverse the stroma, and then be translocated into or across the thylakoid membrane. Protein transport across the envelope requires ATP hydrolysis but not electrical or proton gradients. The energy requirements for the thylakoid translocation step were studied here for the light-harvesting chlorophyll a/b protein (LHCP), an integral membrane protein, and for several thylakoid lumen-resident proteins: plastocyanin and OE33, OE23, and OE17 (the 33-, 23-, and 17-kDa subunits of the oxygen-evolving complex, respectively). Dissipation of the thylakoid protonmotive force during an in organello protein import assay partially inhibited the thylakoid localization of LHCP and OE33, totally inhibited localization of OE23 and OE17, and had no effect on localization of plastocyanin. We used reconstitution assays for LHCP insertion and for OE23 and OE17 transport into isolated thylakoids to investigate the energy requirements in detail. The results indicated that LHCP insertion absolutely requires ATP hydrolysis and is enhanced by a transthylakoid delta pH and that transport of OE23 and OE17 is absolutely dependent upon a delta pH. Surprisingly, OE23 and OE17 transport occurred maximally in the complete absence of ATP. These results establish the thylakoid membrane as the only membrane system in which a delta pH can provide all of the energy required to translocate proteins across the bilayer. They also demonstrate that the energy requirements for integration into or translocation across the thylakoid membranes are protein-specific.     

Chloroplast phosphoproteins. Evidence for a thylakoid-bound phosphoprotein phosphatase

1. Isolated intact pea (Pisum sativum) chloroplasts incorporate [32P]orthophosphate into several thylakoid polypeptides in the light. Transfer of the labelled chloroplasts to darkness results in rapid dephosphorylation of the polypeptides. The most rapidly dephosphorylated phosphoproteins are the 26000-Mr doublet derived from the light-harvesting chlorophyll a/b binding complex. 2. Incubation of isolated 32P-labelled thylakoids in buffer in the absence of stromal components also results in rapid protein dephosphorylation. Again, the most rapidly dephosphorylated phosphoproteins are the 26000-Mr light-harvesting doublet. Dephosphorylation of all thylakoid phosphoproteins is accelerated by addition of up to 10 mM MgCl2. 3. The enzyme responsible for dephosphorylation is a phosphatase rather than a phosphotransferase or the thylakoid protein kinase acting in reverse. The enzyme is specifically and totally inhibited by NaF and does not require phosphoryl group acceptors such as ADP. Unlike the protein kinase, the phosphatase is indifferent to light and the electron transport inhibitor 3(3,4-dichlorophenyl)-1,1-dimethylurea. 4. The phosphorylated regions of the thylakoid phosphoproteins protrude from the outer surface of the membrane and are removed by trypsin treatment.     

叶绿体结构状态与光化学活性的关系

叶绿体被膜阻碍以Fecy为受体的电子传递,而对以DCIP为受体的电子传递无妨。被膜完整度越高则P/O值也越高。类囊体膜结构的完整度高,则电子传递速率和P/O值也比膜结构受到破损时高。类囊体膜结构的完整度对保持PS Ⅱ活性是必要的,随着完整度的降低,PS Ⅱ在电子传递中所占比重相应减少。     

In pea stipules a functional photosynthetic electron flow occurs despite a reduced dynamicity of LHCII association with photosystems

The flexible association of the light harvesting complex II (LHCII) to photosystem (PS) I and PSII to balance their excitation is a major short-term acclimation process of the thylakoid membrane, together with the thermal dissipation of excess absorbed energy, reflected in non-photochemical quenching of chlorophyll fluorescence (NPQ). In Pisum sativum, the leaf includes two main photosynthetic parts, the basal stipules and the leaflets. Since the stipules are less efficient in carbon fixation than leaflets, the adjustments of the thylakoid system, which safeguard the photosynthetic membrane against photodamage, were analysed. As compared to leaflets, the stipules experienced a decay in PSII photochemical activity. The supramolecular organization of photosystems in stipules showed a more conspicuous accumulation of large PSII-LHCII supercomplexes in the grana, but also a tendency to retain the PSI-LHCI-LHCII state transition complex and the PSI-LHCI-PSII-LHCII megacomplexes probably located at the interface between appressed and stroma-exposed membranes. As a consequence, stipules had a lower capacity to perform state transitions and the overall thylakoid architecture was less structurally flexible and ordered than in leaflets. Yet, stipules proved to be quite efficient in regulating the redox state of the electron transport chain and more capable of inducing NPQ than leaflets. It is proposed that, in spite of a relatively static thylakoid arrangement, LHCII interaction with both photosystems in megacomplexes can contribute to a regulated electron flow.     

Effects of DDT on photosynthetic electron flow in Secale species

Following a survey of a range of varieties of rye, mainly Secale cereale, for reaction to DDT, the mode of action of the pesticide in a susceptible variety was studied. Two sites of interaction of DDT with the photosynthetic electron transport chain were demonstrated. The first site of inhibition was on the oxidizing side of photosystem 2, between the sites of electron donation from diphenylcarbazide at pH 6.0 and pH 8.0 in Tris-washed chloroplasts. The second site of DDT inhibition was in the intermediate electron transport chain, and was demonstrated by using dichlorophenol-indophenol and phenyldiamines as electron donors in chloroplasts where electron flow from photosystem 2 was inhibited by 3-(3,4-dichlorophenyl)-1,1-dimethylurea. The sites are distinct from those characteristic of herbicides which affect photosynthetic electron flow.     

Artificial increase of the light-harvesting ability of photosynthetic units in isolated chloroplasts

A synthetic fluorochromous lipid, rhodaminyl triglyceride (rhodaminyl TG), was intercalated into isolated thylakoid membranes of chloroplasts up to 30 molecules per 100 molecules of chlorophyll. As a result of fluorochrome presence, an absorption band appeared in a yellow-green spectrum region, its intensity being comparable with the red and blue chlorophyll bands. The energy absorbed by rhodaminyl TG was transferred through chlorophyll to the reaction centers of photosystems I and II, inducing an additional electron flow of about 30%. Therefore the exogenous fluorochrome dissolved in lipid matrix functions as an accessory pigment which significantly modifies the spectral sensitivity of the photosynthetic process. The energy transfer from rhodaminyl TG to chlorophyll occurs by mechanism of the inductive resonance type.Abbreviations rhodaminyl TG rhodaminyl triglyceride (rac-1,2-dioleoyl-3[11(3-rhodaminyl)amino-undelanoyl]glycerol) - Me₂SO dimethylsulfoxide - PS photosystem - PPC pigment-protein complex - F₀, F_m initial and maximal levels of chlorophyll fluorescence     

Structure, function and regulation of plant photosystem I

Photosystem I (PSI) is a multisubunit protein complex located in the thylakoid membranes of green plants and algae, where it initiates one of the first steps of solar energy conversion by light-driven electron transport. In this review, we discuss recent progress on several topics related to the functioning of the PSI complex, like the protein composition of the complex in the plant Arabidopsis thaliana, the function of these subunits and the mechanism by which nuclear-encoded subunits can be inserted into or transported through the thylakoid membrane. Furthermore, the structure of the native PSI complex in several oxygenic photosynthetic organisms and the role of the chlorophylls and carotenoids in the antenna complexes in light harvesting and photoprotection are reviewed. The special role of the 'red' chlorophylls (chlorophyll molecules that absorb at longer wavelength than the primary electron donor P700) is assessed. The physiology and mechanism of the association of the major light-harvesting complex of photosystem II (LHCII) with PSI during short term adaptation to changes in light quality and quantity is discussed in functional and structural terms. The mechanism of excitation energy transfer between the chlorophylls and the mechanism of primary charge separation is outlined and discussed. Finally, a number of regulatory processes like acclimatory responses and retrograde signalling is reviewed with respect to function of the thylakoid membrane. We finish this review by shortly discussing the perspectives for future research on PSI.     

Enhanced thermal tolerance of photosynthesis and altered chloroplast ultrastructure in a mutant of Arabidopsis deficient in lipid desaturation

A mutant of Arabidopsis thaliana, deficient in activity of the chloroplast n-6 desaturase, accumulated high levels of C_16:1 and C_18:1 lipids and had correspondingly reduced levels of polyunsaturated lipids. The altered lipid composition of the mutant had pronounced effects on chloroplast ultrastructure, thylakoid membrane protein and chlorophyll content, electron transport rates, and the thermal stability of the photosynthetic membranes. The change in chloroplast ultrastructure was due to a 48% decrease in the amount of appressed membranes that was not compensated for by an increased amount of nonappressed membrane. This resulted in a net loss of 36% of the thylakoid membrane per chloroplast and a corresponding reduction in chlorophyll and protein content. Electrophoretic analysis of the chlorophyll-protein complexes further revealed a small decrease in the amount of light-harvesting complex. Relative levels of whole chain and protosystem II electron transport rates were also reduced in the mutant. In addition, the mutation resulted in enhanced thermal stability of photosynthetic electron transport. These observations suggest a central role of polyunsaturated lipids in determining chloroplast structure and maintaining normal photosynthetic function and demonstrate that lipid unsaturation directly affects the thermal stability of photosynthetic membranes.     

Membrane surface potential and the reactivity of the System II primary electron acceptor to charged electron carriers in the medium

A hypothesis is proposed to explain the change in the apparent rate constant for the reaction between the primary electron acceptor of System II situated in the thylakoid membrane and the artificial electron acceptors added in the medium. Dark oxidation rate of the primary acceptor by artificial electron acceptors was monitored by measuring the induction of chlorophyll fluorescence in the presence of an electron transport inhibitor, 3-(3′,4′-dichlorophenyl)-1,1-dimethylurea, in spinach chloroplasts. The apparent rate constant for the oxidation changed widely when the medium pH or salt concentrations were varied, or ionic detergents were added. The change was quantitatively ascribed (1) to the change in the local concentration of electron acceptors at the thylakoid surface due to the electrical potential difference between the surface and the bulk aqueous phase (Gouy-Chapman diffuse double layer theory) and (2) to the situation whereby the apparent rate constant is determined with respect to concentration in the bulk phase.Values for the surface potential in the vicinity of System II were estimated from the change in the apparent rate constant under various conditions. The results closely agreed with those obtained previously from the rate constant of the dark step of the System II-dependent Hill reaction with ferricyanide (Itoh, S. (1978) Plant Cell Physiol. 19, 149–166).Application of the hypothesis to various reactions between the added ionic reagents and the endogenous components in the membrane or between the endogenous components situated in different parts of the membrane is discussed.     

Interplay between ascorbic acid and lipophilic antioxidant defences in chloroplasts of water-stressed Arabidopsis plants

Nitric oxide (NO) is a bioactive molecule involved in diverse physiological functions in plants. Here we demonstrate that NO is capable of regulating the activity of photophosphorylation in chloroplasts. The electron transport activity in photosystem II determined from chlorophyll a fluorescence was inhibited by NO. NO also inhibited light-induced DeltapH formation across the thylakoid membrane. High concentrations of nitrite and nitrate did not show such inhibitory effects, suggesting that the inhibition is not due to uncoupling effects of the oxidized products of NO. ATP synthesis activity upon illumination was severely inhibited by NO (IC(50)=0.7 microM). The inhibition was found to be temporary and the activity was completely recovered by removing NO. Bovine hemoglobin and bicarbonate were effective in preventing NO-dependent inhibition of photophosphorylation. These results indicate that NO is a reversible inhibitor of photosynthetic ATP synthesis.     

Some effects of 4-chloro-5-(dimethylamino)-2-phenyl-3(2H)-pyridazinone (San 9785) on the development of chloroplast thylakoid membranes in Hordeum vulgare L.

Chloroplast ultrastructural and photochemical features were examined in 6-d-old barley (Hordeum vulgare L. cv. Sundance) plants which had developed in the presence of 4-chloro-5-(dimethylamino)-2-phenyl-3(2H)-pyridazinone (San 9785). In spite of a substantial modification of the fatty-acid composition of thylakoid lipids there were no gross abnormalities in chloroplast morphology, and normal amounts of membrane and chlorophyll were present. Fluorescence kinetics at 77K demonstrated considerable energetic interaction of photosystem (PS)I and PSII chlorophylls within the altered lipid environment. An interference with electron transport was indicated from altered room-temperature fluorescence kinetics at 20°C. Subtle changes in the arrangements of chloroplast membranes were consistently evident and the overall effects of these changes was to increase the proportion of appressed to nonappressed membranes. This correlated with a lower chlorophyll a/b ratio, an increase in the amount of light-harvesting chlorophylls as determined by gel electrophoresis and fluorescence emission spectra, and an increase in excitation-energy transfer from PSII to PSI, as predicted from current ideas on the organisation of photosystems in appressed and non-appressed thylakoid membranes.Abbreviations CP1 P700-chlorophyll a protein - F_o, F_m, F_v minimal, maximal and variable fluorescence yield - LHCP light-harvesting chlorophyll-protein complex - PSI, PSII photosystem I, II - San 9785 4-chloro-5(dimethylamino)-2-phenyl-3(2H)-pyridazinone     

Relations between fluorescence and thylakoid structure in Porphyridium cruentum

The increase in chlorophyll a steady-state fluorescence, induced by high NaCl concentration in Porphyridium cruentum in the presence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea, is directly correlated with a significant decrease in thylakoid thickness. It does not appear affected either by alteration of light absorption due to configurational change or by electron transport processes. Oxygen evolution occurs only in intact structures. The interrelationship between membrane structure, oxygen evolution and chlorophyll a steady-state fluorescence is discussed.