Central-Cis isomers of lutein found in the major light-harvesting complex of Photosystem II (LHC IIb) of higher plants

Lutein (,-carotene-3,3-diol) is the major carotenoid of the light-harvesting systems of higher plants. Lutein was isolated at 4°C and in complete darkness from the bulk light-harvesting complex of Photosystem II of spinach (LHC IIb) and from BBY particles. Separation using normal-phase HPLC (with 2D detection) in comparison to the authentic isomers (prepared by iodine-sensitised isomerization) showed the presence of a number of geometrical isomers of this xanthophyll in PS II, namely all-trans (the major component); 13-cis, 13-cis and 15-cis-lutein. Iodine-sensitised photo-isomerization of all-trans lutein produced six geometrical isomers of lutein as determined by HPLC. The configuration of five of these isomers was determined by ¹H-NMR to be all-trans, 9-cis, 9-cis, 13-cis and 13-cis. In addition, small amounts of another isomer have been tentatively identified to be 15-cis lutein on the basis of its electronic absorption spectrum. The possible functional significance of the presence of cis-isomers of this carotenoid in LHC IIb is discussed.     

Heat-induced reversible changes in Photosystem 1 absorption cross-section of pea chloroplasts and sub-chloroplast preparations

Reversible changes in the room temperature fluorescence quenching at 685 nm and light scattering level at 577 nm, indicating about 15% of granal unstacking, induced by high temperature treatment (40°C, for 5 min) of pea chloroplasts were shown. Analysis of the low temperature excitation fluorescence spectra of the 735 nm Photosystem 1 (PS 1) band (F735), in the 635–725 nm region, has revealed the involvement of light-harvesting (LHC 2, maxima at 650 and 676 nm) and the proximal Photosystem 2 antenna (maxima 668, 687 nm) in heat-induced enhancement of the PS 1 long wavelength antenna absorption cross-section. It was found that the two PS 1 sub-chloroplast preparations, achieved by the digitonin method, possessed different characteristics of this enhancement. For the heavier fraction (100 000 g) the additional absorption cross-section was formed mostly at the expense of PS 2 antennas (apparently spillover), but for the lighter PS 1 fraction (145 000 g) the changes have indicated an -transfer mechanism, i.e., participation of only LHC 2 in the energy transfer towards PS 1. This may indicate the heterogeneous character of the temperature-induced energy redistribution across the PS 1-containing chloroplast membrane compartments. The model of heat-induced changes in the pigment-protein complex arrangement is discussed in terms of domain organisation of the thylakoid membrane.Abbreviations Chl a/b ratio between chlorophyll a and chlorophyll b concentrations - CP43 and CP47 proximal Photosystem 2 antenna complexes - D1/D2 complex Photosystem 2 reaction centre complex - EDTA ethylenediaminetetraacetic acid - F685 and F696 Photosystem 2 low temperature fluorescence bands - F735 Photosystem 1 low temperature fluorescence band - Fp free pigment band in green gel electrophoresis - LHC 2 light-harvesting chlorophyll a/b complex - LHCP I, II and III light-harvesting bands in green gel electrophoresis - Cp1 and Cpa bands in green gel electrophoresis which are associated with Photosystem 1 and 2 reaction centre complexes with internal antennas - P700 Photosystem 1 reaction centre - PPC pigment-protein complex - PS 1 and Photosystem 1 alpha and Photosystem 1 beta - PS 2 and Photosystem 2 alpha and Photosystem 2 beta - RC reaction centre - SDS-PAGE sodiumdodecylsulphate-polyacrylamide gel electrophoresis - St1-St2 state-1-state-2 transitions     

Analysis of xanthophyll cycle carotenoids and chlorophyll fluorescence in light intensity-dependent chlorophyll-deficient mutants of wheat and barley

Three light intensity-dependent Chl b-deficient mutants, two in wheat and one in barley, were analyzed for their xanthophyll cycle carotenoids and Chl fluorescence characteristics under two different growth PFDs (30 versus 600 mol photons·m^–2 s^–1 incident light). Mutants grown under low light possessed lower levels of total Chls and carotenoids per unit leaf area compared to wild type plants, but the relative proportions of the two did not vary markedly between strains. In contrast, mutants grown under high light had much lower levels of Chl, leading to markedly greater carotenoid to Chl ratios in the mutants when compared to wild type. Under low light conditions the carotenoids of the xanthophyll cycle comprised approximately 15% of the total carotenoids in all strains; under high light the xanthophyll cycle pool increased to over 30% of the total carotenoids in wild type plants and to over 50% of the total carotenoids in the three mutant strains. Whereas the xanthophyll cycle remained fairly epoxidized in all plants grown under low light, plants grown under high light exhibited a considerable degree of conversion of the xanthophyll cycle into antheraxanthin and zeaxanthin during the diurnal cycle, with almost complete conversion (over 90%) occurring only in the mutants. 50 to 95% of the xanthophyll cycle was retained as antheraxanthin and zeaxanthin overnight in these mutants which also exhibited sustained depressions in PS II photochemical efficiency (F_v/F_m), which may have resulted from a sustained high level of photoprotective energy dissipation activity. The relatively larger xanthophyll cycle pool in the Chl b-deficient mutant could result in part from the reported concentration of the xanthophyll cycle in the inner antenna complexes, given that the Chl b-deficient mutants are deficient in the peripheral LHC-II complexes.Abbreviations A antheraxanthin - Chl chlorophyll - F_o and F_m minimal yield (at open PS II reaction centers) and maximal yield (at closed centers) of chlorophyll fluorescence in darkness - F level of fluorescence during illumination with photosynthetically active radiation - F_m maximal yield (at closed centers) of chlorophyll fluorescence during illumination with photosynthetically active radiation - (F_m–F)/F_m actual efficiency of PS II during illumination with photosynthetically active radiation - F_v/F_m+(F_m–F_o)/F_m intrinsic efficiency of PS II in darkness - LHC_II light-harvesting chlorophyll-protein complex of Photosystem II - PFD photon flux density (between 400 and 700 nm) - PS I Photosystem I - PS II Photosystem II - V violaxanthin - Z zeaxanthin     

9-Aminoacridine and dibucaine exhibit competitive interactions and complicated inhibitory effects that interfere with measurements of ΔpH and xanthophyll cycle-dependent Photosystem II energy dissipation

This study concerns measurements and interpretations of the trans-thylakoid membrane pH gradient, pH, and xanthophyll cycle-dependent energy dissipation in Photosystem II (PS II). Compared and contrasted are the concentration-dependent inhibitory effects and interactions between two lipophilic tertiary amines, namely, 9-aminoacridine the pH indicator and dibucaine a local anesthetic reported to inhibit both the pH and xanthophyll cycle deepoxidation. Chlorophyll a fluorescence monitored both electron transport efficiency and xanthophyll cycle-dependent energy dissipation, high-performance liquid chromatography monitored deepoxidase and chloroplast ATPase activities and steady-state fluorescence monitored various activities of the amines in solution. Low concentrations (up to 2 M) of both 9-aminoacridine and dibucaine showed similar fluorescence properties and pH-dependent uptake into thylakoids. Importantly both amines exhibited mutually competitive inhibitory effects with respect to this pH-dependent uptake and fluorescence quenching. The fluorescence yields of both compounds in aqueous solution were strongly quenched by sodium ascorbate, a necessary cofactor for in vitro deepoxidation. Both compounds similarly inhibited several light induced activities including deepoxidation, photosynthetic electron transport and PS II energy dissipation. However, for all these activities 9-aminoacridine was 2 to 5 times more potent. Importantly, 9-aminoacridine inhibited deepoxidation with an I₅₀1 M, a concentration far below that which inhibits the pH, ATP synthesis/hydrolysis or electron transport. The inhibitory effects of both compounds on PS II energy dissipation were exerted at 3 to 5 times lower concentration if added before as opposed to after a saturating level of deepoxidation. This result confirms the important role for deepoxidation in mediating PS II energy dissipation. Compared to 9-aminoacridine and in contrast to similar effects on the light-induced activities, dibucaine exhibited significantly different inhibitory effects on ATPase activity and ATPase mediated PS II energy dissipation. However, we conclude from the more potent inhibition by 9-aminoacridine and the similar inhibitory patterns of all the light-induced activities that neither 9-aminoacridine nor dibucaine possess unique capacities to neutralize the light-mediated pH. DCMU–3-(3,4-dichlorophenyl)-1,1-dimethylurea; DTT–dithiothreitol; f_x–fractional intensity of fluorescence lifetime component x; F()_m–maximal PS II Chl a fluorescence intensity with all Q_A reduced in the absence (presence) of thylakoid membrane energization; F_o–minimal PS II Chl a fluorescence intensity with all Q_A oxi dized; F_s–steady state PS II Chl a fluorescence; HPLC–high performance liquid chromatography; I_(o)–intensity of fluorescence in the presence (absence) of quencher; K_a–association constant between Z (and A) and protonated PS II units; LA–local anesthetic; NaAsc–sodium ascorbate; NR–neutral red; PAM–pulse-amplitude modulation fluorometer; PFD–photon-flux density, mols photons m^-2 s^-1; PS I–Photosystem I; PS II–Photosystem II; [PS II^-+]–concentration of PS II units with inactive/deprotonated (active/protonated ) xanthophyll binding sites; [PS II_tot]–total concentration of PS II units; [PS II⁺-Z]–concentration of PS II units with Z or A bound; Q–fraction of fluorescence intensity that is quenched; Q_max–fraction of fluorescence intensity that is quenched under control conditions; Q_A–primary quinone electron acceptor of PS II; V–violaxanthin; Z–zeaxanthin; 9AA–9-aminoacridine; pH–trans-thylakoid membrane proton gradient; _f–lifetime of Chl a fluorescence     

The coleoptile chloroplast: Distinct distribution of xanthophyll cycle pigments,and enrichment in Photosystem II

Recent studies have shown that coleoptile chloroplasts operate the xanthophyll cycle, and that their zeaxanthin concentration co-varies with their sensitivity to blue light. The present study characterized the distribution of photosynthetic pigments in thylakoid pigment–protein complexes from dark-adapted and light-treated coleoptile and mesophyll chloroplasts, the low temperature fluorescence emission spectra, and the rates of PS I and PS II electron transport in both types of chloroplasts from 5-day-old corn seedlings. Pigments were extracted from isolated PS I holocomplex, LHC IIb trimeric and LHC II monomeric complexes and analyzed by HPLC. Chlorophyll distribution in coleoptile thylakoids showed 31% of the total collected Chl in PS I and 65% in the light harvesting complexes of PS II. In mesophyll thylakoids, the values were 44% and 54%, respectively. Mesophyll and coleoptile PS I holocomplexes differed in their Chl t a/Chl t b ratios (8.1 and 6.1, respectively) and -carotene content. In contrast, mesophyll and coleoptile LHC IIb trimers and LHC II monomers had similar Chl t a/Chl t b ratios and -carotene content. The three analyzed pigment–protein complexes from dark-adapted coleoptile chloroplasts contained zeaxanthin, whereas there was no detectable zeaxanthin in the complexes from dark-adapted mesophyll chloroplasts. In both chloroplast types, zeaxanthin and antheraxanthin increased markedly in the three pigment–protein complexes upon illumination, while violaxanthin decreased. In mesophyll thylakoids, zeaxanthin distribution as a percentage of the xanthophyll cycle pool was: LHC II monomers > LHC IIb trimers > PS I holocomplex, and in coleoptile thylakoids, it was: LHC IIb trimers > LHC II monomers = PS I holocomplex. Low temperature (77 K) fluorescence emission spectra showed that the 686 nm emission of coleoptile chloroplasts was approximately 50% larger than that of mesophyll chloroplasts when normalized at 734 nm. The pigment and fluorescence analysis data suggest that there is relatively more PS II per PS I and more LHC I per CC I in coleoptile chloroplasts than in mesophyll chloroplasts. Measurements of t in vitro uncoupled photosynthetic electron transport showed approximately 60% higher rates of electron flow through PS II in coleoptile chloroplasts than in mesophyll chloroplasts. Electron transport rates through PS I were similar in both chloroplast types. Thus, when compared to mesophyll chloroplasts, coleoptile chloroplasts have a distinct PS I pigment composition, a distinct chlorophyll distribution between PS I and PS II, a distinct zeaxanthin percentage distribution among thylakoid pigment–protein complexes, a higher PS II-related fluorescence emission, and higher PS II electron transport capacity. These characteristics may be associated with a sensory transducing role of coleoptile chloroplasts.     

Functional size of Photosystem II determined by radiation inactivation

The functional size of Photosystem II (PS II) was investigated by radiation inactivation. The technique provides an estimate of the functional mass required for a specific reaction and depends on irradiating samples with high energy -rays and assaying the remaining activity. The analysis is based on target theory that has been modified to take into account the temperature dependence of radiation inactivation of proteins. Using PS II enriched membranes isolated from spinach we determined the functional size of primary charge separation coupled to water oxidation and quinone reduction at the Q_B site: H₂O (Mn)₄ Y_z P680 Pheophytin Q phenyl-p-benzoquinone. Radiation inactivation analysis indicates a functional mass of 88 ± 12 kDa for electron transfer from water to phenyl-p-benzoquinone. It is likely that the reaction center heterodimer polypeptides, D1 and D2, contribute approximately 70 kDa to the functional mass, in which case polypeptides adding up to approximately 20 kDa remain to be identified. Likely candidates are the and subunits of cytochrome b ₅₅₉and the 4.5 kDa psbI gene product.Abbreviations Cyt cytochrome - PS Photosystem - P680 primary electron donor of Photosystem II - Q_A primary quinone acceptor of Photosystem II - Q_B secondary quinone acceptor of Photosystem II - Y_z tyrosine donor to P680     

Photosynthetic electron transport and carbon-reduction-cycle enzyme activities under long-term drought stress in Casuarina equisetifolia Forst. & Forst.

The inhibition of photosynthetic electron transport and the activity of photosynthetic carbon reduction cycle (PCR) enzymes under long-term water stress after slow dehydration was studied in non-nodulated Casuarina equisetifolia Forst. & Forst. plants. Initially, drought increased the fraction of closed Photosystem II (PS II) reaction centres (lowered qP) and decreased the quantum yield of PS II electron transport (_PSII) with no enhancement of non-radiative dissipation of light energy (qN) because it increased the efficiency of electron capture by open PS II centres (F_v/F_m). As drought progressed, F_v/F_m fell and the decrease in _PSII was associated with an increased qN. The kinetics of dark relaxation of fluorescence quenching pointed to an increase in a slowly-relaxing component under drought, in association with increased contents of zeaxanthin and antheraxanthin. Total NADP-dependent malate dehydrogenase activity increased and total stromal fructose-1,6-bisphosphatase activity decreased under drought, while the activation state of these enzymes remained unchanged. Water stress did not alter the activity and the activation state of ribulose bisphosphate carboxylase oxygenase.     

The carotenoid zeaxanthin and ‘high-energy-state quenching’ of chlorophyll fluorescence

The possibility that zeaxanthin mediates the dissipation of an excess of excitation energy in the antenna chlorophyll of the photochemical apparatus has been tested through the use of an inhibitor of violaxanthin de-epoxidation, dithiothreitol (DTT), as well as through the comparison of two closely related organisms (green and blue-green algal lichens), one of which (blue-green algal lichen) naturally lacks the xanthophyll cycle. In spinach leaves, DTT inhibited a major component of the rapidly relaxing high-energy-state quenching' of chlorophyll fluorescence, which was associated with a quenching of the level of initial fluorescence (F₀) and exhibited a close correlation with the zeaxanthin content of leaves when fluorescence quenching was expressed as the rate constant for radiationless energy dissipation in the antenna chlorophyll. Green algal lichens, which possess the xanthophyll cycle, exhibited the same type of fluorescence quenching as that observed in leaves. Two groups of blue-green algal lichens were used for a comparison with these green algal lichens. A group of zeaxanthin-free blue-green algal lichens did not exhibit the type of chlorophyll fluorescence quenching indicative of energy dissipation in the pigment bed. In contrast, a group of blue-green algal lichens which had formed zeaxanthin slowly through reactions other than the xanthophyll cycle, did show a very similar response to that of leaves and green algal lichens. Fluorescence quenching indicative of radiationless energy dissipation in the antenna chlorophyll was the predominant component of high-energy-state quenching in spinach leaves under conditions allowing for high rates of steady-state photosynthesis. A second, but distinctly different type of high-energy-state quenching of chlorophyll fluorescence, which was not inhibited by DTT (i.e., it was zeaxanthin independent) and which is possibly associated with the photosystem II reaction center, occurred in addition to that associated with zeaxanthin in leaves under a range of conditions which were less favorable for linear photosynthetic electron flow. In intact chloroplasts isolated from (zeaxanthin-free) spinach leaves a combination of these two types of rapidly reversible fluorescence quenching occurred under all conditions examined.Abbreviations DTT dithiothreitol - F₀ (or F₀) yield of instantaneous fluorescence at open PS II reaction centers in the dark (or during actinic illumination) - F_M (or F_M) yield of maximum fluorescence induced by a saturation pulse of light in the dark (or during actinic illumination) - F_V (or F_V) yield of variable fluorescence induced by a saturating pulse of light in the dark (or during actinic illumination) - k _D rate constant for radiationless energy dissipation in the antenna chlorophyll - SV Stern-Volmer equation - PFD photon flux density - PS I photosystem I - PS II photosystem II - Q_A acceptor of photosystem II - q_N coefficient of nonphotochemical chlorophyll fluorescence quenching - q_P coefficient of photochemical chlorophyll fluorescence quenching     

Polygonal inequalities as a key to neuronic equations

Neuronic or decision equations, first proposed as a mathematical model of neural activity, have shown, after their exact, compact solution was found, typical behaviours that make them natural tools for General Systems studies. It is shown here that their mathematical investigation is remarkably furthered by generalizing the triangular inequality to polygonal ones. These permit the immediate computation of the tensorial expansion of linearly separable boolean functions, and exhibit clearly the connection between their continuous and discontinuous aspects.     

Ecological theories and Dutch nature conservation

This paper aims to achieve insight into various ecological theories in the Netherlands which have different, and sometimes opposing, views on the conservation of nature. Interviews, publications and archival research brought to light four separate theories: vitalistic/holistic, dynamic, cybernetic and chaos. Diversity is reached through stability according to vitalistic/holistic and cybernetic theories, but through change and instablility according to the dynamic and chaos theories. These two groups are working apart, and continue to have their own ideas. Prediction of the future is only possible with the vitalistic/holistic and cybernetic theories. Ecologists who adhere to these theories feel responsible and able in different ways to change ecological nature towards desirable end goals. The other two theories, dynamic and chaos, appear to be less activist.     

Immunofluorescence localization of the epidermolytic toxin target in mouse epidermal cells and tissue

Summary An epidermolytic toxin target was observed in keratohyalin granules of sectioned epidermis by a direct fluorescence procedure using FTC-toxin, but not by an indirect procedure using sequential reaction with toxin, anti-toxin and FTC-secondary antibody. The investigation of the two procedures was extended to keratinocytes. A dispase digestion procedure yielded three fractions which corresponded to basal, spinous and granular cells according to biochemical and morphological criteria. It was shown that the direct and indirect procedures both detected the toxin target in the keratohyalin granules of granular cells, but that the indirect procedure was very insensitive. In control experiments, the profilaggrin of keratohyalin granules was detected readily in cells by a direct procedure using FTC-antiprofilaggrin but only weakly by an indirect double antibody procedure. Insensitivity to indirect procedures thus appears to be a particular property of the keratohyalin granule site. It was shown that the toxin target was readily accessible in permeable (trypsin-isolated) granular cells but inaccessible in impermeable (dispase-isolated) cells.     

Observations on the fine structure of the cercaria of Notocotylus attenuatus and formation of the cyst wall of the metacercaria

Summary The dorsal tegument of the mature cercaria of Notocotylus attenuatus is a syncytial, cytoplasmic layer, containing two types of secretory granule which are identifiable ultrastructurally. The type 1 secretory bodies are electron lucid, whereas most type 2 granules have a banded appearance. The ventral tegument contains granules which are secreted from the type 3 cells; the type 3 granules are membrane bound, electron dense, and consist of both an amorphous and a finely striated zone. The type 4 cells mainly contain cigar-shaped granules consisting of an amorphous core surrounded by concentric striations. The granules exhibit structural variability in shape and content. The type 4 cells undergo a cellular migration to the tegument during encystment. The structure of the posterior-lateral glands and mode of secretion of the granules are described. Possible functions of microtubules are discussed for each cell type. Details of some secretory processes involved in the formation of the hemispherical cyst wall are described. The layers of the cyst wall may be related to the granular contents of the various parenchymal cells of the cercaria. The tegument of the metacercaria originates primarily from the cytoplasm of the type 1, type 2, type 3 and type 4 cells.     

Molecular mapping of a new gene Rrs4 CI 11549 for resistance to barley scald (Rhynchosporium secalis)

Doubled haploid (DH) progeny from a cross between the scald susceptible barley (Hordeum vulgare L.) cultivar Ingrid and the resistant accession CI 11549 (Nigrinudum) was evaluated for resistance in the pathogen Rhynchosporium secalis (Oudem) J.J. Davis. Two linked and incompletely dominant loci confer resistance CI 11549 against isolate 4004. One is an allele at the complex Rrs1 locus on chromosome 3H close to the centromere; the other is located 22 cM distally on the long arm. The latter locus is designated Rrs4. In BC₃-lines into Ingrid from CI 2222 (another Nigrinudum) resistance seems governed by one locus close to the telomeric region of chromosome 7H, probably allelic to Rrs2. In neither case did we find any trace of the recessive gene rh8 reported to be present in Nigrinudum. Various resistance donors of Ethiopian origin designated as Nigrinudum, Jet or Abyssinian were identical to a great extent with respect to markers, but differed in resistance to different isolates of scald or in barley yellow dwarf virus (BYDV) resistance. The implications for their use as differentials in scald tests and screening of germplasm collections are discussed.     

Fluorescence studies on interaction between phospho-LHC II and subchloroplast Photosystem 1 preparations

Chloroplast proteins were phosphorylated under two test conditions: white light irradiance alone and white light irradiance with the addition of glucose and glucose oxidase, used to produce an anaerobic medium. The interaction of phospho-LHC II with Photosystem 1 (PS 1) was studied for two types of PS I preparation. Changes in the chlorophyll a/b ratio and the ratio of 650 and 680 nm band intensities (E650/E680) in fluorescence excitation spectra were used in calculating the phospho-LHC II portion which became associated with PS 1. It is shown that the associated portion of phospho-LHC II varies for each of the PS 1 preparations and phosphorylation procedures. Possible conclusions as regards the transfer of various sets of LHC II subpopulations under different phosphorylation procedures and the differences of interaction with PS 1 are discussed.Abbreviations PS 1 Photosystem 1 - PS 2 Photosystem 2 - LHC II light-harvesting chlorophyll a/b protein complex II - Chl chlorophyll - fluorescence quantum yield - _f life time of fluorescence at =685 nm - F735 fluorescence band with a maximum at 735 nm - F685 fluorescence band with a maximum at 685 nm - E650/E680 ratio of amplitudes in excitation fluorescence spectrum at 650 and 680 nm     

High frequency of triplicated α-globin loci and absence or low frequency of α thalassemia in Polynesian Samoans

Summary Most of the population in certain areas of Melanesia have one -globin gene deletion ( thal₂). It is thought that the high frequencies of thal₂ in this population is due to a selective advantage given by malaria infection to carriers of thal₂. We are interested in neighboring Polynesia which, although adjacent to Melanesia, has always been free of malaria due to the absence of the vector anopheles. We studied 60 Polynesian Samoans and 150 Malaysians by restriction endonuclease gene mapping using Eco RI, Bam HI, and Bgl II and hybridization to ³²P-labeled -globin gene probe. Seven among the 60 (11.7%) Samoans had triplicated -globin loci type 1, while none had thal₂. On digestion with Bgl II the third -globin gene was found in an additional 3.7kb fragment in all seven Samoans with triplicated -globin loci, while digestion with Bam HI produced an abnormal elongated 18.2 kb fragment carrying -globin genes in addition to the normal 14.5 kb fragment. None of the Polynesian Samoans had thal₂ or thal₁. Only two of the Malaysians had triplicated -globin loci.     

Changes in the quantities of violaxanthin de-epoxidase,xanthophylls and ascorbate in spinach upon shift from low to high light

Zeaxanthin, a carotenoid in the xanthophyll cycle, has been suggested to play a role in the protection against photodestruction. We have studied the importance of the parameters involved in zeaxanthin formation by comparing spinach plants grown in low light (100 to 250 mol m^-2 s^-1) to plants transferred to high light (950 mol m^-2 s^-1). Different parameters were followed for a total of 11 days. Our experiments show that violaxanthin de-epoxidase decreased between 15 and 30%, the quantity of xanthophyll cycle pigments doubled to 100 mmol (mol Chl)^-1, corresponding to 27 mol m^-2, and the rate of violaxanthin to zeaxanthin conversion was doubled. Lutein and neoxanthin increased from 50 to 71 mol m^-2 and from 16 to 23 mol m^-2, respectively. On a leaf area basis, chlorophyll and -carotene levels first decreased and then after 4 days increased. The chlorophyll a/b ratio was unchanged. The quantity of ascorbate was doubled to 2 mmol m^-2, corresponding to an estimated increase in the chloroplasts from 25 to 50 mM. In view of our data, we propose that the increase in xanthophyll cycle pigments and ascorbate only partly explain the increased rate of conversion of violaxanthin to zeaxanthin, but the most probable explanation of the faster conversion is an increased accessibility of violaxanthin in the membrane.     

Leaf Xanthophyll content and composition in sun and shade determined by HPLC

As a part of our investigations to test the hypothesis that zeaxanthin formed by reversible de-epoxidation of violaxanthin serves to dissipate any excessive and potentially harmful excitation energy we determined the influence of light climate on the size of the xanthophyll cycle pool (violaxanthin + antheraxanthin + zeaxanthin) in leaves of a number of species of higher plants. The maximum amount of zeaxanthin that can be formed by de-epoxidation of violaxanthin and antheraxanthin is determined by the pool size of the xanthophyll cycle. To quantitate the individual leaf carotenoids a rapid, sensitive and accurate HPLC method was developed using a non-endcapped Zorbax ODS column, giving baseline separation of lutein and zeaxanthin as well as of other carotenoids and Chl a and b.The size of the xanthophyll cycle pool, both on a basis of light-intercepting leaf area and of light-harvesting chlorophyll, was ca. four times greater in sun-grown leaves of a group of ten sun tolerant species than in shade-grown leaves in a group of nine shade tolerant species. In contrast there were no marked or consistent differences between the two groups in the content of the other major leaf xanthophylls, lutein and neoxanthin. Also, in each of four species examined the xanthophyll pool size increased with an increase in the amount of light available during leaf development whereas there was little change in the content of the other xanthophylls. However, the -carotene/-carotene ratio decreased and little or no -carotene was detected in sun-grown leaves. Among shade-grown leaves the -carotene/-carotene ratio was considerably higher in species deemed to be umbrophilic than in species deemed to be heliophilic.The percentage of the xanthophyll cycle pool present as violaxanthin (di-epoxy-zeaxanthin) at solar noon was 96–100% for shade-grown plants and 4–53% for sun-grown plants with zeaxanthin accounting for most of the balance. The percentage of zeaxanthin in leaves exposed to midday solar radiation was higher in those with low than in those with high photosynthetic capacity.The results are consistent with the hypothesis that the xanthophyll cycle is involved in the regulation of energy dissipation in the pigment bed, thereby preventing a buildup of excessive excitation energy at the reaction centers.Abbreviations A antheraxanthin - C -carotene - C -carotene - EPS epoxidation state (V+0.5A)/(V+A+Z) - L lutein - N neoxanthin - PFD photon flux density - V violaxanthin - Z zeaxanthin C.I.W.-D.P.B. Publiation No. 1035     

Sequence- and Regio-Selectivity in the Montmorillonite-Catalyzed Synthesis of RNA

The six binary montmorillonite clay-catalyzed reactions of the5-phosphorimidazolides of adenosine, cytidine, guanosine anduridine were performed and the eight dimers from each reactionwere separated and analyzed by HPLC. A 16–51-fold higher yieldof the 5-purine-pyrimidine dimers over that of the5-pyrimidine-purines was observed. The total yield of the5-purine-pyrimidine dimers was in the 50–70% range while thatof the 5-pyrimidine-purine dimers was 1.3–7.0%. Less sequenceselectivity was observed in the homodimers formed.Regioselectivity for the formation of 3, 5-phosphodiesterbonds over that found in the absence of clay was observed. The5-purine-pyrimidine, 5-pyrimidine-pyrimidine and5-purine-purine dimers had 3, 5-links in about half of theirphosphodiester bonds. The percent phosphodiester links in the5-pyrimidine-pyrimidine dimers was 18%, a value close to thatobserved in the absence of the montmorillonite catalyst. Themontmorillonite-catalyzed reaction of all four activatednucleotides was performed and the 24 products were separated andanalyzed. The trends observed in the binary reactions wereconfirmed and the results also showed that the relativereactivity of the activated monomers was A>G>C>U in theratio 8.2: 4.8: 1.3: 1 respectively. No 5-pyrimidine-purineswith a 5-U and pG³pU, pC³pAand pC³pG weredetected. These studies suggest that a limited population ofRNAs would have formed in catalyzed prebiotic reactions.     

Evaluation of the role of State transitions in determining the efficiency of light utilisation for CO2 assimilation in leaves

Wheat leaves were exposed to light treatments that excite preferentially Photosystem I (PS I) or Photosystem II (PS II) and induce State 1 or State 2, respectively. Simultaneous measurements of CO₂ assimilation, chlorophyll fluorescence and absorbance at 820 nm were used to estimate the quantum efficiencies of CO₂ assimilation and PS II and PS I photochemistry during State transitions. State transitions were found to be associated with changes in the efficiency with which an absorbed photon is transferred to an open PS II reaction centre, but did not correlate with changes in the quantum efficiencies of PS II photochemistry or CO₂ assimilation. Studies of the phosphorylation status of the light harvesting chlorophyll protein complex associated with PS II (LHC II) in wheat leaves and using chlorina mutants of barley which are deficient in this complex demonstrate that the changes in the effective antennae size of Photosystem II occurring during State transitions require LHC II and correlate with the phosphorylation status of LHC II. However, such correlations were not found in maize leaves. It is concluded that State transitions in C₃ leaves are associated with phosphorylation-induced modifications of the PS II antennae, but these changes do not serve to optimise the use of light absorbed by the leaf for CO₂ assimilation.Abbreviations Fm, Fo, Fv maximal, minimal and variable fluorescence yields - Fm, Fv maximal and variable fluorescence yields in a light adapted state - LHC II light harvesting chlorophyll a/b protein complex associated with PS II - q_P photochemical quenching - A₈₂₀ light-induced absorbance change at 820 nm - _{PS I}, _{PS II} relative quantum efficiencies of PS I and PS II photochemistry - _{CO 2} quantum yield of CO₂ assimilation     

Integrins: cell adhesives and modulators of cell function

Summary Integrins encompass a family of cell-surface molecules which play a crucial role in cell-cell and cell-extracellular matrix interaction. Of these heterodimeric transmembrane glycoproteins (consisting of an and chain) as yet at least 20 different types have been described, all with a different pattern of reactivity with extracellular matrix components. In this review the cell and tissue distribution of the integrins is discussed, with special emphasis on immunohistochemical localization of the ₁ integrins and the ₆₄ integrin. The ₁ integrins comprise a subfamily in which eight chains combine with one (the ₁) chain. The ₂₁, ₃₁ and ₆₁ and the ₆₄ integrins are expressed on a wide variety of epithelia on the basolateral surface or exclusively on the basal surface facing the basement membrane (e.g. ₆₁ and ₆₄). Leucocyte integrins, which share a common ₂ chain, occur almost exclusively on white blood cells and their precursors. The vitronectin receptors, which share a common _v chain, occur in a wide variety of cell types. Integrins play a major role in the interaction of the cell with the extracellular matrix in order to create and maintain tissue architecture. It has become clear, however, that through integrin-ligand interaction cell function is also modulated. Furthermore, in pathological conditions integrins play a role of some significance. Integrins mediate leucocyte traffic in developing inflammatory processes and function in neoplastic growth when it comes to invasion and metastasis.