Xanthophyll

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Roberto Bassi - One of the best experts on this subject based on the ideXlab platform.

  • Different Roles of α- and β-Branch Xanthophylls in Photosystem Assembly and Photoprotection
    Journal of Biological Chemistry, 2007
    Co-Authors: Luca Dall'osto, Giovanni Giuliano, Alessia Fiore, Stefano Cazzaniga, Roberto Bassi
    Abstract:

    Abstract Xanthophylls (oxygenated carotenoids) are essential components of the plant photosynthetic apparatus, where they act in photosystem assembly, light harvesting, and photoprotection. Nevertheless, the specific function of individual Xanthophyll species awaits complete elucidation. In this work, we analyze the photosynthetic phenotypes of two newly isolated Arabidopsis mutants in carotenoid biosynthesis containing exclusively α-branch (chy1chy2lut5) or β-branch (chy1chy2lut2) Xanthophylls. Both mutants show complete lack of qE, the rapidly reversible component of nonphotochemical quenching, and high levels of photoinhibition and lipid peroxidation under photooxidative stress. Both mutants are much more photosensitive than npq1lut2, which contains high levels of viola- and neoxanthin and a higher stoichiometry of light-harvesting proteins with respect to photosystem II core complexes, suggesting that the content in light-harvesting complexes plays an important role in photoprotection. In addition, chy1chy2lut5, which has lutein as the only Xanthophyll, shows unprecedented photosensitivity even in low light conditions, reduced electron transport rate, enhanced photobleaching of isolated LHCII complexes, and a selective loss of CP26 with respect to chy1chy2lut2, highlighting a specific role of β-branch Xanthophylls in photoprotection and in qE mechanism. The stronger photosystem II photoinhibition of both mutants correlates with the higher rate of singlet oxygen production from thylakoids and isolated light-harvesting complexes, whereas carotenoid composition of photosystem II core complex was not influential. In depth analysis of the mutant phenotypes suggests that α-branch (lutein) and β-branch (zeaxanthin, violaxanthin, and neoxanthin) Xanthophylls have distinct and complementary roles in antenna protein assembly and in the mechanisms of photoprotection.

  • Mechanistic aspects of the Xanthophyll dynamics in higher plant thylakoids
    Physiologia Plantarum, 2003
    Co-Authors: Tomas Morosinotto, Stefano Caffarri, Luca Dall'osto, Roberto Bassi
    Abstract:

    Plant thylakoids have a highly conserved Xanthophyll composition, consisting of β-carotene, lutein, neoxanthin and a pool of violaxanthin that can be converted to antheraxanthin and zeaxanthin in excess light conditions. Recent work has shown that Xanthophylls undergo dynamic changes, not only in their composition but also in their distribution among Lhc proteins. Xanthophylls are released from specific binding site in the major trimeric LHCII complex of photosystem II and are subsequently bound to different sites into monomeric Lhcb proteins and dimeric Lhca proteins. In this work we review available evidence from in vivo and in vitro studies on the structural determinants that control Xanthophyll exchange in Lhc proteins. We conclude that the Xanthophyll exchange rate is determined by the structure of individual Lhc gene products and it is specifically controlled by the lumenal pH independently from the activation state of the violaxanthin deepoxidase enzyme. The Xanthophyll exchange induces important modifications in the organization of the antenna system of Photosystem II and, possibly of Photosystem I. Major changes consist into a modulation of the light harvesting efficiency and an increase of the protection from lipid peroxidation. The Xanthophyll cycle thus appears to be a signal transduction system for co-ordinated regulation of the photoprotection mechanisms under persistent stress from excess light.

  • dynamics of chromophore binding to lhc proteins in vivo and in vitro during operation of the Xanthophyll cycle
    Journal of Biological Chemistry, 2002
    Co-Authors: Tomas Morosinotto, Roberta Baronio, Roberto Bassi
    Abstract:

    Abstract Three plant Xanthophylls are components of the Xanthophyll cycle in which, upon exposure of leaves to high light, the enzyme violaxanthin de-epoxidase (VDE) transforms violaxanthin into zeaxanthin via the intermediate antheraxanthin. Previous work (1) showed that Xanthophylls are bound to Lhc proteins and that substitution of violaxanthin with zeaxanthin induces conformational changes and fluorescence quenching by thermal dissipation. We have analyzed the efficiency of different Lhc proteins to exchange violaxanthin with zeaxanthin both in vivo and in vitro. Light stress of Zea mays leaves activates VDE, and the newly formed zeaxanthin is found primarily in CP26 and CP24, whereas other Lhc proteins show a lower exchange capacity. The de-epoxidation system has been reconstituted in vitro by using recombinant Lhc proteins, recombinant VDE, and monogalactosyl diacylglycerol (MGDG) to determine the intrinsic capacity for violaxanthin-to-zeaxanthin exchange of individual Lhc gene products. Again, CP26 was the most efficient in Xanthophyll exchange. Biochemical and spectroscopic analysis of individual Lhc proteins after de-epoxidation in vitro showed that Xanthophyll exchange occurs at the L2-binding site. Xanthophyll exchange depends on low pH, implying that access to the binding site is controlled by a conformational change via lumenal pH. These findings suggest that the Xanthophyll cycle participates in a signal transduction system acting in the modulation of light harvestingversus thermal dissipation in the antenna system of higher plants.

  • the major antenna complex of photosystem ii has a Xanthophyll binding site not involved in light harvesting
    Journal of Biological Chemistry, 2001
    Co-Authors: Stefano Caffarri, Roberta Croce, Jacques Breton, Roberto Bassi
    Abstract:

    We have characterized a Xanthophyll binding site, called V1, in the major light harvesting complex of photosystem II, distinct from the three tightly binding sites previously described as L1, L2, and N1. Xanthophyll binding to the V1 site can be preserved upon solubilization of the chloroplast membranes with the mild detergent dodecyl-alpha-d-maltoside, while an IEF purification step completely removes the ligand. Surprisingly, spectroscopic analysis showed that when bound in this site, Xanthophylls are unable to transfer absorbed light energy to chlorophyll a. Pigments bound to sites L1, L2, and N1, in contrast, readily transfer energy to chlorophyll a. This result suggests that this binding site is not directly involved in light harvesting function. When violaxanthin, which in normal conditions is the main carotenoid in this site, is depleted by the de-epoxidation in strong light, the site binds other Xanthophyll species, including newly synthesized zeaxanthin, which does not induce detectable changes in the properties of the complex. It is proposed that this Xanthophyll binding site represents a reservoir of readily available violaxanthin for the operation of the Xanthophyll cycle in excess light conditions.

  • Photochemical behavior of Xanthophylls in the recombinant photosystem II antenna complex, CP26.
    Biochemistry, 2001
    Co-Authors: Harry A. Frank, Roberta Croce, Somes K. Das, James A. Bautista, Doug Bruce, Sergej Vasil'ev, Massimo Crimi, Roberto Bassi
    Abstract:

    The steady state absorption and fluorescence spectroscopic properties of the Xanthophylls, violaxanthin, zeaxanthin, and lutein, and the efficiencies of singlet energy transfer from the individual Xanthophylls to chlorophyll have been investigated in recombinant CP26 protein overexpressed in Escherichia coli and then refolded in vitro with purified pigments. Also, the effect of the different Xanthophylls on the extents of static and dynamic quenching of chlorophyll fluorescence has been investigated. Absorption, fluorescence, and fluorescence excitation demonstrate that the efficiency of light harvesting from the Xanthophylls to chlorophyll a is relatively high and insensitive to the particular Xanthophyll that is present. A small effect of the different Xanthophylls is observed on the extent of quenching of Chl fluorescence. The data provide the precise wavelengths of the absorption and fluorescence features of the bound pigments in the highly congested spectral profiles from these light-harvesting complexes. This information is important in assessing the mechanisms by which higher plants dissipate excess energy in light-harvesting proteins.

Elizabeth J Johnson - One of the best experts on this subject based on the ideXlab platform.

  • Xanthophyll lutein zeaxanthin content in fruits vegetables and corn and egg products
    Journal of Food Composition and Analysis, 2009
    Co-Authors: Alisa Perry, Helen Rasmussen, Elizabeth J Johnson
    Abstract:

    Lutein and zeaxanthin are carotenoids that are selectively taken up into the macula of the eye where they are thought to protect against the development of age-related macular degeneration. Current dietary databases make it difficult to ascertain their individual roles in eye health because their concentrations in foods are generally reported together. The objective of this work is to determine the concentrations of lutein and zeaxanthin, separately, within major food sources of dietary Xanthophylls as determined by NHANES 2001-2002 intakes. Corn and corn products were found to be major contributors of dietary zeaxanthin whereas green leafy vegetables were major contributors of dietary lutein. The predominant isomeric Xanthophyll form was trans for all foods. Processed foods contained more cis Xanthophyll isomers than fruits and vegetables. These data will provide added information to the current databases for lutein and zeaxanthin content of commonly consumed foods as well as enhance the validity of estimates of dietary intake of these Xanthophylls and their respective contributions to health.

  • the selective retention of lutein meso zeaxanthin and zeaxanthin in the retina of chicks fed a Xanthophyll free diet
    Experimental Eye Research, 2007
    Co-Authors: Yingming Wang, Sonja L Connor, Elizabeth J Johnson, William E Connor
    Abstract:

    Abstract Lutein and zeaxanthin are pigmented oxygenated carotenoids, or Xanthophylls, derived from plants and concentrated in the retina of primates and birds. We investigated the transport, distribution and depletion of lutein and zeaxanthin in the plasma and tissues of newly hatched chicks fed Xanthophyll-free diets. One-day-old Leghorn chicks were randomly divided into two groups. A control group was fed a diet containing lutein and zeaxanthin (5.2 and 1.7 mg/kg diet, respectively) for 28 days. An experimental group was fed a diet containing no lutein and zeaxanthin for 28 days. Plasma and tissues were analyzed for lutein and zeaxanthin at 28 days (control) and on days 1, 14 and 28 (experimental). At hatching, lutein and zeaxanthin were the predominant carotenoids present in the blood and tissues. As indicated by their similar mass contents, there was complete transfer of these carotenoids from egg yolk to chick. Lutein and zeaxanthin concentrations in the plasma and tissues of chicks fed the Xanthophyll-free diet decreased rapidly to almost zero (with a depletion time of seven days [ t 1/2 ]). In contrast, the retina retained its initial concentrations of lutein and zeaxanthin similar to the control group. meso -Zeaxanthin and cis -zeaxanthin were identified only in the retina. The retina concentrated zeaxanthin over lutein. Lutein and zeaxanthin were selectively retained in the retinas of chicks fed a Xanthophyll-free diet. In contrast, the plasma and other tissues lost up to 90% of their original content of Xanthophylls. These data emphasize the relative stability of lutein and zeaxanthin in the cone-rich retina where they are present as esters in oil droplets. The tissue depletion suggests the need for a regular dietary intake of lutein and zeaxanthin because of rapid depletion in the body. It is clear that these Xanthophylls may have an essential role in the cone-rich retina of the chick as evidenced by their selective retention.

  • nutritional manipulation of primate retinas iii effects of lutein or zeaxanthin supplementation on adipose tissue and retina of Xanthophyll free monkeys
    Investigative Ophthalmology & Visual Science, 2005
    Co-Authors: Elizabeth J Johnson, Martha Neuringer, Robert M Russell, Wolfgang Schalch, Max D Snodderly
    Abstract:

    PURPOSE. Macular pigment (MP) is composed of the Xanthophylls lutein (L) and zeaxanthin (Z) and may help to prevent age-related macular degeneration or retard its progression. In this study the effects of L or Z supplementation on carotenoid levels was examined in serum, adipose tissue, and retina in rhesus monkeys with no previous intake of Xanthophylls. METHODS. From birth to 7 to 16 years of age, 18 rhesus monkeys were fed semipurified diets containing all essential nutrients but no Xanthophylls. Six were supplemented with pure L and 6 with pure Z at 3.9 mol/kg per day for 24 to 101 weeks. At baseline and at 4- to 12-week intervals, carotenoids in adipose tissue were measured by HPLC. At study completion, carotenoids in serum and retina (central 4 mm, 8-mm annulus, and the periphery) were determined. Results were compared with data from control monkeys fed a standard laboratory diet. RESULTS. Monkeys fed Xanthophyll-free diets had no L or Z in serum or tissues. After L or Z supplementation, serum and adipose tissue concentrations significantly increased in the supplemented groups. Both L and 3R,3S-Z (RSZ or meso-Z, not present in the diet) were incorporated into retinas of monkeys supplemented with L, with RSZ present only in the macula (central 4 mm). All-trans Z, but no RSZ, accumulated in retinas of monkeys supplemented with Z. CONCLUSIONS. L is the precursor of RSZ, a major component of macular pigment. Xanthophyll-free monkeys can accumulate retinal Xanthophylls and provide a valuable model for examining their uptake and conversion. (Invest Ophthalmol Vis Sci. 2005;46:692‐702) DOI:10.1167/iovs.02-1192

  • nutritional manipulation of primate retinas i effects of lutein or zeaxanthin supplements on serum and macular pigment in Xanthophyll free rhesus monkeys
    Investigative Ophthalmology & Visual Science, 2004
    Co-Authors: Martha Neuringer, Elizabeth J Johnson, Marita M Sandstrom, Max D Snodderly
    Abstract:

    PURPOSE The Xanthophylls lutein (L) and zeaxanthin (Z) are the primary components of macular pigment (MP) and may protect the macula from age-related degeneration (AMD). In this study, L or Z was fed to rhesus monkeys reared on Xanthophyll-free diets to follow the accumulation of serum carotenoids and MP over time. METHODS Eighteen rhesus monkeys were fed Xanthophyll-free semipurified diets from birth until 7 to 16 years. The diets of six were then supplemented with pure L and six with pure Z at 3.9 micromol/kg per day (2.2 mg/kg per day) for 24 to 56 weeks. At baseline and 4- to 12-week intervals during supplementation, serum carotenoids were measured by HPLC, and MP density was estimated by two-wavelength reflectometry. Serum carotenoids and MP were also measured in monkeys fed a stock diet. RESULTS Monkeys fed Xanthophyll-free diets had no L or Z in serum and no detectable MP. During supplementation, serum L or Z increased rapidly over the first 4 weeks and from 16 weeks onward maintained similar levels, both several times higher than in stock-diet-fed monkeys. The central peak of MP optical density increased to a relatively steady level by 24 to 32 weeks in both L- and Z-fed groups. Rhesus monkeys fed a stock diet had lower blood concentrations of L than those found in humans and other nonhuman primates. CONCLUSIONS Rhesus monkeys respond to either dietary L or Z supplementation with increases in serum Xanthophylls and MP, even after life-long Xanthophyll deficiency. These animals provide a potential model to study mechanisms of protection from AMD.

Adam M Gilmore - One of the best experts on this subject based on the ideXlab platform.

  • psbs dependent enhancement of feedback de excitation protects photosystem ii from photoinhibition
    Proceedings of the National Academy of Sciences of the United States of America, 2002
    Co-Authors: Xiaoping Li, Adam M Gilmore, Patricia Mullermoule, Krishna K. Niyogi
    Abstract:

    Feedback de-excitation (qE) regulates light harvesting in plants to prevent inhibition of photosynthesis when light absorption exceeds photosynthetic capacity. Although the mechanism of qE is not completely understood, it is known to require a low thylakoid lumen pH, de-epoxidized Xanthophylls, and the photosystem II protein PsbS. During a short-term 4-h exposure to excess light, three PsbS- and qE-deficient Arabidopsis thaliana mutants that differed in Xanthophyll composition were more photoinhibited than the wild type. The extent of photoinhibition was the same in all of the mutants, suggesting that qE capacity rather than Xanthophyll composition is critical for photoprotection in short-term high light, in contrast to longer-term high light conditions (days) when additional antioxidant roles of specific Xanthophylls are evident. Plants with a 2-fold increase in qE capacity were generated by overexpression of PsbS, demonstrating that the level of PsbS limits the qE capacity in wild-type Arabidopsis. These results are consistent with the idea that variations in PsbS expression are responsible for species-specific and environmentally induced differences in qE capacity observed in nature. Furthermore, plants with higher qE capacity were more resistant to photoinhibition than the wild type. Increased qE was associated with decreased photosystem II excitation pressure and changes in the fractional areas of chlorophyll a fluorescence lifetime distributions, but not the lifetime centers, suggesting that qE protects from photoinhibition by preventing overreduction of photosystem II electron acceptors. Engineering of qE capacity by PsbS overexpression could potentially yield crop plants that are more resistant to environmental stress.

  • photosystem ii chlorophyll a fluorescence lifetimes and intensity are independent of the antenna size differences between barley wild type and chlorina mutants photochemical quenching and Xanthophyll cycle dependent nonphotochemical quenching of fluo
    Photosynthesis Research, 1996
    Co-Authors: Adam M Gilmore, Theodore L Hazlett, Peter G Debrunner
    Abstract:

    Photosystem II (PS II) chlorophyll (Chl) a fluorescence lifetimes were measured in thylakoids and leaves of barley wild-type and chlorina f104 and f2 mutants to determine the effects of the PS II Chl a+b antenna size on the deexcitation of absorbed light energy. These barley chlorina mutants have drastically reduced levels of PS II light-harvesting Chls and pigment-proteins when compared to wild-type plants. However, the mutant and wild-type PS II Chl a fluorescence lifetimes and intensity parameters were remarkably similar and thus independent of the PS II light-harvesting antenna size for both maximal (at minimum Chl fluorescence level, Fo) and minimal rates of PS II photochemistry (at maximum Chl fluorescence level, Fm). Further, the fluorescence lifetimes and intensity parameters, as affected by the trans-thylakoid membrane pH gradient (ΔpH) and the carotenoid pigments of the Xanthophyll cycle, were also similar and independent of the antenna size differences. In the presence of a ΔpH, the Xanthophyll cycle-dependent processes increased the fractional intensity of a Chl a fluorescence lifetime distribution centered around 0.4–0.5 ns, at the expense of a 1.6 ns lifetime distribution (see Gilmore et al. (1995) Proc Natl Acad Sci USA 92: 2273–2277). When the zeaxanthin and antheraxanthin concentrations were measured relative to the number of PS II reaction center units, the ratios of fluorescence quenching to [Xanthophyll] were similar between the wild-type and chlorina f104. However, the chlorina f104, compared to the wild-type, required around 2.5 times higher concentrations of these Xanthophylls relative to Chl a+b to obtain the same levels of Xanthophyll cycle-dependent fluorescence quenching. We thus suggest that, at a constant ΔpH, the fraction of the short lifetime distribution is determined by the concentration and thus binding frequency of the Xanthophylls in the PS II inner antenna. The ΔpH also affected both the widths and centers of the lifetime distributions independent of the Xanthophyll cycle. We suggest that the combined effects of the Xanthophyll cycle and ΔpH cause major conformational changes in the pigment-protein complexes of the PS II inner or core antennae that switch a normal PS II unit to an increased rate constant of heat dissipation. We discuss a model of the PS II photochemical apparatus where PS II photochemistry and Xanthophyll cycle-dependent energy dissipation are independent of the Peripheral antenna size.

  • Carotenoids 3: in vivo function of carotenoids in higher plants.
    The FASEB Journal, 1996
    Co-Authors: Barbara Demmig-adams, Adam M Gilmore, William W. Adams
    Abstract:

    The function of the long-chain, highly unsaturated carotenoids of higher plants in photoprotection is becoming increasingly well understood, while at the same time their function in other processes, such as light collection, needs to be reexamined. Recent progress in this area has been fueled by more accurate determinations of the photophysical properties of these molecules, as well as extensive characterization of the physiology and ecology of a particular group of carotenoids, those of the Xanthophyll cycle, that play a key role in the photoprotection of photosynthesis under environmental stress. The deepoxidized Xanthophylls zeaxanthin and antheraxanthin, together with a low pH within the photosynthetic membrane, facilitate the harmless dissipation of excess excitation energy directly within the light-collecting chlorophyll antennae. Evidence for this function as well as current contrasting hypotheses concerning its molecular mechanism are reviewed. In addition, the acclimation of the Xanthophyll cycle...

  • Xanthophyll cycle dependent quenching of photosystem ii chlorophyll a fluorescence formation of a quenching complex with a short fluorescence lifetime
    Proceedings of the National Academy of Sciences of the United States of America, 1995
    Co-Authors: Adam M Gilmore, Theodore L Hazlett
    Abstract:

    Abstract Excess light triggers protective nonradiative dissipation of excitation energy in photosystem II through the formation of a trans-thylakoid pH gradient that in turn stimulates formation of zeaxanthin and antheraxanthin. These Xanthophylls when combined with protonation of antenna pigment-protein complexes may increase nonradiative dissipation and, thus, quench chlorophyll a fluorescence. Here we measured, in parallel, the chlorophyll a fluorescence lifetime and intensity to understand the mechanism of this process. Increasing the Xanthophyll concentration in the presence of a pH gradient (quenched conditions) decreases the fractional intensity of a fluorescence lifetime component centered at approximately 2 ns and increases a component at approximately 0.4 ns. Uncoupling the pH gradient (unquenched conditions) eliminates the 0.4-ns component. Changes in the Xanthophyll concentration do not significantly affect the fluorescence lifetimes in either the quenched or unquenched sample conditions. However, there are differences in fluorescence lifetimes between the quenched and unquenched states that are due to pH-related, but nonXanthophyll-related, processes. Quenching of the maximal fluorescence intensity correlates with both the Xanthophyll concentration and the fractional intensity of the 0.4-ns component. The unchanged fluorescence lifetimes and the proportional quenching of the maximal and dark-level fluorescence intensities indicate that the Xanthophylls act on antenna, not reaction center processes. Further, the fluorescence quenching is interpreted as the combined effect of the pH gradient and Xanthophyll concentration, resulting in the formation of a quenching complex with a short (approximately 0.4 ns) fluorescence lifetime.

  • Epoxidation of zeaxanthin and antheraxanthin reverses non-photochemical quenching of photosystem II chlorophyll a fluorescence in the presence of trans-thylakoid ΔpH
    FEBS Letters, 1994
    Co-Authors: Adam M Gilmore, Narendranath Mohanty, Harry Y. Yamamoto
    Abstract:

    Abstract The Xanthophyll cycle apparently aids the photoprotection of photosystem II by regulating the nonradiative dissipation of excess absorbed light energy as heat. However, it is a controversial question whether the resulting nonphotochemical quenching is soley dependent on Xanthophyll cycle activity or not. The Xanthophyll cycle consists of two enzymic reactions, namely deepoxidation of the diepoxide violaxanthin to the epoxide-free zeaxanthin and the much slower, reverse process of epoxidation. While deepoxidation requires a transthylakoid pH gradient (ΔpH), epoxidation can proceed irrespective of a ΔpH. Herein, we compared the extent and kinetics of deepoxidation and epoxidation to the changes in fluorescence in the presence of a light-induced thylakoid ΔpH. We show that epoxidation reverses fluorescence quenching without affecting thylakoid ΔpH. These results suggest that epoxidase activity reverses quenching by removing deepoxidized Xanthophyll cycle pigments from quenching complexes and converting them to a nonquenching form. The transmembrane organization of the Xanthophyll cycle influences the localization and the availability of deepoxidized Xanthophylls is to support nonphotochemical quenching capacity. The results confirm the view that rapidly reversible nonphotochemical quenching is dependent on deepoxidized Xanthophyll.

Max D Snodderly - One of the best experts on this subject based on the ideXlab platform.

  • nutritional manipulation of primate retinas iii effects of lutein or zeaxanthin supplementation on adipose tissue and retina of Xanthophyll free monkeys
    Investigative Ophthalmology & Visual Science, 2005
    Co-Authors: Elizabeth J Johnson, Martha Neuringer, Robert M Russell, Wolfgang Schalch, Max D Snodderly
    Abstract:

    PURPOSE. Macular pigment (MP) is composed of the Xanthophylls lutein (L) and zeaxanthin (Z) and may help to prevent age-related macular degeneration or retard its progression. In this study the effects of L or Z supplementation on carotenoid levels was examined in serum, adipose tissue, and retina in rhesus monkeys with no previous intake of Xanthophylls. METHODS. From birth to 7 to 16 years of age, 18 rhesus monkeys were fed semipurified diets containing all essential nutrients but no Xanthophylls. Six were supplemented with pure L and 6 with pure Z at 3.9 mol/kg per day for 24 to 101 weeks. At baseline and at 4- to 12-week intervals, carotenoids in adipose tissue were measured by HPLC. At study completion, carotenoids in serum and retina (central 4 mm, 8-mm annulus, and the periphery) were determined. Results were compared with data from control monkeys fed a standard laboratory diet. RESULTS. Monkeys fed Xanthophyll-free diets had no L or Z in serum or tissues. After L or Z supplementation, serum and adipose tissue concentrations significantly increased in the supplemented groups. Both L and 3R,3S-Z (RSZ or meso-Z, not present in the diet) were incorporated into retinas of monkeys supplemented with L, with RSZ present only in the macula (central 4 mm). All-trans Z, but no RSZ, accumulated in retinas of monkeys supplemented with Z. CONCLUSIONS. L is the precursor of RSZ, a major component of macular pigment. Xanthophyll-free monkeys can accumulate retinal Xanthophylls and provide a valuable model for examining their uptake and conversion. (Invest Ophthalmol Vis Sci. 2005;46:692‐702) DOI:10.1167/iovs.02-1192

  • nutritional manipulation of primate retinas i effects of lutein or zeaxanthin supplements on serum and macular pigment in Xanthophyll free rhesus monkeys
    Investigative Ophthalmology & Visual Science, 2004
    Co-Authors: Martha Neuringer, Elizabeth J Johnson, Marita M Sandstrom, Max D Snodderly
    Abstract:

    PURPOSE The Xanthophylls lutein (L) and zeaxanthin (Z) are the primary components of macular pigment (MP) and may protect the macula from age-related degeneration (AMD). In this study, L or Z was fed to rhesus monkeys reared on Xanthophyll-free diets to follow the accumulation of serum carotenoids and MP over time. METHODS Eighteen rhesus monkeys were fed Xanthophyll-free semipurified diets from birth until 7 to 16 years. The diets of six were then supplemented with pure L and six with pure Z at 3.9 micromol/kg per day (2.2 mg/kg per day) for 24 to 56 weeks. At baseline and 4- to 12-week intervals during supplementation, serum carotenoids were measured by HPLC, and MP density was estimated by two-wavelength reflectometry. Serum carotenoids and MP were also measured in monkeys fed a stock diet. RESULTS Monkeys fed Xanthophyll-free diets had no L or Z in serum and no detectable MP. During supplementation, serum L or Z increased rapidly over the first 4 weeks and from 16 weeks onward maintained similar levels, both several times higher than in stock-diet-fed monkeys. The central peak of MP optical density increased to a relatively steady level by 24 to 32 weeks in both L- and Z-fed groups. Rhesus monkeys fed a stock diet had lower blood concentrations of L than those found in humans and other nonhuman primates. CONCLUSIONS Rhesus monkeys respond to either dietary L or Z supplementation with increases in serum Xanthophylls and MP, even after life-long Xanthophyll deficiency. These animals provide a potential model to study mechanisms of protection from AMD.

Stefano Caffarri - One of the best experts on this subject based on the ideXlab platform.

  • Mechanistic aspects of the Xanthophyll dynamics in higher plant thylakoids
    Physiologia Plantarum, 2003
    Co-Authors: Tomas Morosinotto, Stefano Caffarri, Luca Dall'osto, Roberto Bassi
    Abstract:

    Plant thylakoids have a highly conserved Xanthophyll composition, consisting of β-carotene, lutein, neoxanthin and a pool of violaxanthin that can be converted to antheraxanthin and zeaxanthin in excess light conditions. Recent work has shown that Xanthophylls undergo dynamic changes, not only in their composition but also in their distribution among Lhc proteins. Xanthophylls are released from specific binding site in the major trimeric LHCII complex of photosystem II and are subsequently bound to different sites into monomeric Lhcb proteins and dimeric Lhca proteins. In this work we review available evidence from in vivo and in vitro studies on the structural determinants that control Xanthophyll exchange in Lhc proteins. We conclude that the Xanthophyll exchange rate is determined by the structure of individual Lhc gene products and it is specifically controlled by the lumenal pH independently from the activation state of the violaxanthin deepoxidase enzyme. The Xanthophyll exchange induces important modifications in the organization of the antenna system of Photosystem II and, possibly of Photosystem I. Major changes consist into a modulation of the light harvesting efficiency and an increase of the protection from lipid peroxidation. The Xanthophyll cycle thus appears to be a signal transduction system for co-ordinated regulation of the photoprotection mechanisms under persistent stress from excess light.

  • the major antenna complex of photosystem ii has a Xanthophyll binding site not involved in light harvesting
    Journal of Biological Chemistry, 2001
    Co-Authors: Stefano Caffarri, Roberta Croce, Jacques Breton, Roberto Bassi
    Abstract:

    We have characterized a Xanthophyll binding site, called V1, in the major light harvesting complex of photosystem II, distinct from the three tightly binding sites previously described as L1, L2, and N1. Xanthophyll binding to the V1 site can be preserved upon solubilization of the chloroplast membranes with the mild detergent dodecyl-alpha-d-maltoside, while an IEF purification step completely removes the ligand. Surprisingly, spectroscopic analysis showed that when bound in this site, Xanthophylls are unable to transfer absorbed light energy to chlorophyll a. Pigments bound to sites L1, L2, and N1, in contrast, readily transfer energy to chlorophyll a. This result suggests that this binding site is not directly involved in light harvesting function. When violaxanthin, which in normal conditions is the main carotenoid in this site, is depleted by the de-epoxidation in strong light, the site binds other Xanthophyll species, including newly synthesized zeaxanthin, which does not induce detectable changes in the properties of the complex. It is proposed that this Xanthophyll binding site represents a reservoir of readily available violaxanthin for the operation of the Xanthophyll cycle in excess light conditions.

  • Lhc proteins and the regulation of photosynthetic light harvesting function by Xanthophylls.
    Photosynthesis Research, 2000
    Co-Authors: Roberto Bassi, Stefano Caffarri
    Abstract:

    Photoprotection of the chloroplast is an important component of abiotic stress resistance in plants. Carotenoids have a central role in photoprotection. We review here the recent evidence, derived mainly from in vitro reconstitution of recombinant Lhc proteins with different carotenoids and from carotenoid biosynthesis mutants, for the existence of different mechanisms of photoprotection and regulation based on Xanthophyll binding to Lhc proteins into multiple sites and the exchange of chromophores between different Lhc proteins during exposure of plants to high light stress and the operation of the Xanthophyll cycle. The use of recombinant Lhc proteins has revealed up to four binding sites in members of Lhc families with distinct selectivity for Xanthophyll species which are here hypothesised to have different functions. Site L1 is selective for lutein and is here proposed to be essential for catalysing the protection from singlet oxygen by quenching chlorophyll triplets. Site L2 and N1 are here proposed to act as allosteric sites involved in the regulation of chlorophyll singlet excited states by exchanging ligand during the operation of the Xanthophyll cycle. Site V1 of the major antenna complex LHC II is here hypothesised to be a deposit for readily available substrate for violaxanthin de-epoxidase rather than a light harvesting pigment. Moreover, Xanthophylls bound to Lhc proteins can be released into the lipid bilayer where they contribute to the scavenging of reactive oxygen species produced in excess light.