Photosynthetic Pigments

11 Key excerpts on "Photosynthetic Pigments"

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  Biochemical Aspects Of Plant Physiology

  Technology And Methodology

  • Bhattacharya, A. Vijaya Luxmi(Authors)
  • 2021(Publication Date)
  • NEW INDIA PUBLISHING AGENCY (NIPA)

    (Publisher)

  C HAPTER 13 Plant Pigments Biological pigments, also known simply as pigments or biochromes are substances produced by living organisms that have a colour resulting from selective colour absorption. Biological pigments include plant pigments and flower pigments. Many biological structures, such as skin, eyes, fur and hair contain pigments such as melanin in specialized cells called chromatophores. Pigment colour differs from structural colour in that it is the same for all viewing angles, whereas structural colour is the result of selective reflection or iridescence, usually because of multilayer structures. For example, butterfly wings typically contain structural colour, although many butterflies have cells that contain pigment as well. Biological Pigments  Heme/porphyrin-based: chlorophyll, bilirubin, hemocyanine, hemoglobin, myoglobin  Light-emitting: luciferin  Carotenoids:  Hematochromes (algal pigments, mixes of carotenoids and their derivates)  Carotenes: alpha and beta carotene, lycopene, rhodopsin  Xanthophylls: canthaxanthin, zeaxamthin, lutein  Proteinaceous: phytochrome, phycobiliproteins  Polyene enolates: a class of red pigments unique to parrots  Other: melanin, urochrome, flavonoids. 402 Biochemical Aspects of Plant Physiology: Technology & Methodology 13.1. Pigments in Plants The primary function of pigments in plants is photosynthesis, which uses the green pigment chlorophyll along with several red and yellow pigments that help to capture as much light energy as possible. Other functions of pigments in plants include attracting insects to flowers to encourage pollination. Plant pigments include a variety of different kinds of molecule, including porphyrins, carotenoids, anthocyanins and betalains. All biological pigments selectively absorb certain wavelengths of light while reflecting others.

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  Herbicides and Plant Physiology

  • Andrew H. Cobb(Author)
  • 2022(Publication Date)
  • Wiley-Blackwell

    (Publisher)

  Chapter 6 Inhibitors of Pigment Biosynthesis

  More energy is expended for the weeding out of man’s crops than for any other single human task. LeRoy Holm (1971)

  6.1 Introduction: structures and functions of Photosynthetic Pigments

  Photosynthesis relies on the unique light‐harvesting abilities of the chlorophyll and carotenoid pigments to trap solar energy in the chloroplast thylakoids and transfer excitation energy to the reaction centres. The principal light‐harvesting pigment is chlorophyll a which contains a light‐absorbing ‘head’, centred on a magnesium ion, and a hydrophobic ‘tail’ attached to proteins and lipids, and embedded in the thylakoid membrane. Light is absorbed at the rate of about one photon per chlorophyll molecule per second and an electron is boosted to an excited state for each photon absorbed.

  The light‐harvesting complexes contain two other types of pigment in addition to chlorophyll a, namely chlorophyll b and the carotenoids. These so‐called accessory pigments absorb light of shorter (i.e. higher‐energy) wavelengths than does chlorophyll a, so they increase the width of the spectrum available for photosynthesis. Energy transfer occurs in the sequence: carotenoids, chlorophyll b, chlorophyll a, reaction centre.

  Chlorophylls a and b are found in the leaves of all higher plants and in green algae, typically at a concentration of 0.5 g m−2 of leaf area. Chlorophyll b differs from chlorophyll a in having a formyl group (–CHO) instead of a methyl group (–CH3 ) on one of the N‐containing rings that make up the head group, as indicated in Figure 6.1 . The carotenoids are abundant in green tissues and over 600 have been found in Nature.

  Herbicides that interfere with the biosynthesis of chlorophylls or carotenoids are generally termed ‘bleaching herbicides’ because bleaching (or whitening, i.e. a lack of typically green pigmentation) is a principal symptom in treated plants. Bleaching herbicides were the most frequently patented class of herbicides in the 1980s and the 1990s.

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  Chemical Biomarkers in Aquatic Ecosystems

  • Thomas S. Bianchi, Elizabeth A. Canuel(Authors)
  • 2011(Publication Date)
  • Princeton University Press

    (Publisher)

  12. Photosynthetic Pigments: Chlorophylls, Carotenoids, and Phycobilins

  12.1 Background

  The primary Photosynthetic Pigments used in absorbing photosynthetically active radiation (PAR) are chlorophylls, carotenoids, and phycobilins —with chlorophyll representing the dominant photosynthetic pigment (Emerson and Arnold, 1932a,b; Clayton, 1971, 1980). Although a greater amount of chlorophyll is found on land, 75% of the global turnover (ca. 109 Mgyr–1 ) occurs in oceans, lakes, and rivers/estuaries (Brown et al., 1991; Jeffrey and Mantoura, 1997). All of the light-harvesting pigments are bound to proteins, making up distinct carotenoid and chlorophyll–protein complexes. These pigment–protein complexes in algae and higher plants are located in the thylakoid membrane of chloroplasts (Cohen et al., 1995). The photosynthesizing ability of eukaryotes was made possible by one or more endosymbiotic associations between heterotrophic eukaryotes and photosynthetic prokaryotes (or their descendents) (Gray, 1992; Whatley, 1993). Several primary endosymbioses occurred between eukaryotes and cyanobacteria. In one of the lineages, the photosynthetic organism lost much of its genetic independence and became functionally and genetically integrated as plastids—chloroplasts within the host cell (Kuhlbrandt et al., 1994). At least two types of protists—chloroarachniophytes and cryptomonads—acquired plastids by forming symbioses with eukaryotic algae.

  Photosynthetic organisms have a variety of accessory pigments, on which their classification has been based. Despite this variation, it is generally accepted that all chloroplasts are derived from a single cyanobacterial ancestor. Prochlorophytes are prokaryotes that perform oxygenic photosynthesis using chlorophyll b, like land plants and green algae (Chlorophyta), and were proposed to be the ancestors of chlorophyte chloroplasts. However, three known prochlorophytes (Prochloron didemni, Prochlorothrix hollandica, and Prochlorococcus marinus ) have been shown not to be the specific ancestors of chloroplasts, but only diverged members of the cyanobacteria, which contain phycobilins but lack chlorophyll b (Olson and Pierson, 1987). Consequently, it has been proposed that the ability to synthesize chlorophyll b developed independently several times in prochlorophytes and in the ancestor of chlorophytes. Phylogenetic analyses show that these genes share a common evolutionary origin. This indicates that the progenitors of oxygenic photosynthetic bacteria, including the ancestor of chloroplasts, had both chlorophyll b

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  Integument, Pigments, and Hormonal Processes

  Volume 9: Integument, Pigments and Hormonal Processes

  • (Author)
  • 2012(Publication Date)
  • Academic Press

    (Publisher)

  5 Structural and Biological Aspects of Pigments WALTER GHIDALIA I. Introduction 301 II. Pigments with a Respiratory Function 302 A. The Oxygen-Carrying Pigments 302 B. The Hydrogen Ion and Electron-Carrying Pigments 341 III. Pigments with a Chromatic Function 347 A. The Carotenoids 347 B. The Melanins and Ommochromes 360 IV. Pigments with a Visual Function 364 A. The Reflecting Pigments: Pterins 365 B. The Visual Pigment: Rhodopsin 369 V. Conclusions 373 References 375 I. INTRODUCTION Etymologically speaking, the word pigment, from the Latin term, pigmen-turn, which refers to painting materials and make-up, implies a notion of color. Consequently, organic substances that generally appear colored are considered pigments, although some may at times be colorless, for instance, hemocyanin, when it is deoxygenated. These photosensitive compounds play important roles in living organisms by coloring the body, tissues, or biological fluids, thereby allowing chro-301 302 Walter Ghidalia matic adaptation to natural surroundings, and also by assuming various physiological functions, as in respiration or vision. The study of these compounds represents a field of wide-ranging investi-gation that is impossible to review within the narrow limits of a single chapter. Emphasis will thus be placed on specific aspects of these sub-stances, particularly their structure and functions, and, where possible, the relationships existing between structure and functions. II. PIGMENTS WITH A RESPIRATORY FUNCTION Respiration consists of a series of processes through which organic foodstuffs are oxidized, thus providing organisms with chemical energy. In aerobic respiration, metabolic substrates, generally carbohydrates, are con-verted into carbon dioxide and hydrogen atoms, or their electron equiv-alents.

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  Plant Pigments, Flavors and Textures

  • Shobhit Kumar Singh(Author)
  • 2020(Publication Date)
  • Delve Publishing

    (Publisher)

  Chlorophyll ‘a’ is the most abundant type of pigment in leaves and is, therefore, the most important type of pigment in the chloroplast. Chlorophyll ‘a’ at a molecular level has a porphyrin ring that absorbs light energy. Chlorophyll b Chlorophyll ‘b’ is the less available in nature than the chlorophyll ‘a’, but chlorophyll ‘b’ has the ability to absorb a wider wavelength of light energy. Chlorophyll c Chlorophyll ‘c’ is mostly not found in plants, but it could be found in some microorganisms that are capable of performing photosynthesis. Carotenoid and Phycobilin Carotenoid pigments are popularly found in various photosynthetic organisms and in various plants. These pigments mostly absorb light between Functions and Applications of Plant Pigments, Textures and Flavors 155 the wavelengths of 460 and 550 nm because of which these pigments appear orange, red and yellow in color. Phycobilin is a type of water-soluble pigment which is found in chloroplasts. 6.3. PIGMENTS AND ROLE IN ENERGY TRANSFERS The major role of pigments in photosynthesis is that they play an important role in the absorption of energy from light. There are several free electrons that are present at the molecular level in the chemical structure of these Photosynthetic Pigments which might revolve at different energy levels. If the light energy or the photons of light falls on these pigments the electrons will absorb this energy and might jump to the next energy level. These electrons will continue to remain in the high energy level, and this is not a state of stable energy level because of which during photosynthesis these high-energy electrons might transfer their energy to several other molecules or these electrons themselves would get transferred to other molecules. Therefore, it indicates that these electrons will release the energy that is captured from light.

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  Physicochemical and Plant Physiology

  • Park Nobel(Author)
  • 2012(Publication Date)
  • Academic Press

    (Publisher)

  On the other hand, cyanobacteria, algae, and higher plants produce 0 2 as a photosynthetic product, so they must contain carotenoids to survive in the light. In addition, daily cycles in specific carotenoids can occur, as β-carotene and certain xanthophylls are oxidized during the daytime and then reduced back to the original form at night (Demmig-Adams et al., 1989). Because such oxidations tend to increase with time, the fraction of carot-enoids in the form of xanthophylls generally increases in leaves as the growing season progresses (Czeczuga, 1987; Kirk and Tilney-Bassett, 1978). Other Photosynthetic Pigments 2 5 9 H O O C C O O H I I C H , C H 2 C H 2 C H 2 I I I II C H , C H C H , C H 2 C H 2 C H , C H , C H Phycoerythrobilin H O O C C O O H I I C H , C H 2 C H 7 C H , ι ι ι -I C H , C H C H , C H 2 C H 2 C H , C H , C H 2 J: Η Η Η Phycocyanobilin Figure 5.6 Structure of five important accessory pigments. The phycobilins (lower two structures) occur covalently bound to proteins; i.e., they are the chromophores for phycobiliproteins. H , C C H , Jj^* JK^^^^< ^ J L J 1 1 C H , C H , H ^ C C H < /^-carotene H , C . ^ O H H , C C H , ^ ^ H , Ύ Τ JL JL C H , C H , H ^ C C H * Lutein C H , ii L ^ N ^ C O C H , H , C C H , ^ H , ^ > < ^ y ^ ^ ^ ^ ^ ^ C H , JL JL° ° C H , C H , H O ^ ^ C H , Fucoxanthin 2 6 0 Photochemistry of Photosynthesis Phycobilins The other main accessory pigments important in photosynthesis are the phyco-bilins. Lemberg in the 1920s termed these molecules phycobilins because they occur in algae (red algae and blue-green algae, the latter now referred to as cyanobacteria; phyco is derived from the Greek for seaweed) but they structurally resemble bile pigments. Like the chlorophylls, the phycobilins are tetrapyrroles. However, the four pyrroles in the phycobilins occur in an open chain, as is the case for phytochrome, not in a closed porphyrin ring, as is the case for the chlorophylls.

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  The Chemistry of Plants

  Perfumes, Pigments and Poisons

  • Margareta Séquin(Author)
  • 2021(Publication Date)
  • Royal Society of Chemistry

    (Publisher)

  Whether plant pigments are water-soluble or not determines where in the cells they are stored. Pigments that dissolve in water are stored in the vacuoles in plant cells (see Figure 1.23 in Chapter 1). Anthocyanins and betalains, and also tannins and flavones, have numerous OH groups in their molecules that can easily form hydrogen bonds with water. In addition, some of their OH groups are bonded to sugars, making them glycosides. Therefore, these pigments are soluble in water. In contrast, pigments like chlorophyll and carotenes that have no (or very few) OH groups do not dissolve in water but are fat-soluble. They are stored in their own cell organelles: chlorophyll in chloroplasts and carotenes in chromoplasts.

  The colors of plants that we see are the result of mixtures of pigments. One of the pigments may be dominant, like chlorophyll in green leaves. Structural colors, caused by plant structures like a rough surface or fine hairs on leaves, can contribute to the color shade of a plant part. But they are not as dominant in plants as, for example, in bird feathers or the wings of butterflies where structural colors create many of the colors that we see.5

  For further illustration of plant pigments, Box 4.1 takes a combined look at scents, pigments, and nectars of flowers as attractants for pollinators, and Box 4.2 reflects on the pigments in fall coloration.

  Let us explore now the different families of plant pigments and learn about their special characteristics.

  4.2 The Chlorophylls

  In Chapter 1 we encountered chlorophyll a , the main photosynthetic pigment (Figure 1.26, 1.1 ). There are other types of chlorophylls that distinguish themselves by slight variations in their molecular structures (Figure 4.2 ). All chlorophylls have porphyrin rings, with long sequences of conjugated double bonds, and with a magnesium atom in the center of the ring. The differences are in some of the side chains attached to the porphyrin ring. (R and R′ in Figure 4.2 point out the sites where the differences are.) These variations lead to the absorption of different wavelengths of light—and to a slightly different color of the pigment. A side chain that adds an additional double bond in the conjugated bond pattern enhances absorption of light toward longer wavelengths. Note that chlorophyll b (Figure 4.2 , 4.1 ) has an aldehyde (or CHO) group replacing one of the methyl (CH3 ) groups. The aldehyde group, with a double bond between the carbon and oxygen, is written out for clarity in the figure. If you check the absorption spectra in Figure 1.28, you can compare the wavelengths of maximum absorption for chlorophyll a and b . Note that in chlorophyll b they are shifted toward longer wavelengths. Chlorophyll b serves as an accessory pigment in green plants as it broadens the range of light that is available for photosynthesis. Other chlorophylls and related pigments are found in algae or in cyanobacteria. Pigments of photosynthesizing organisms that live in water need to be able to make use of light energy that is available in their environment. Researchers recently discovered a new type of chlorophyll in cyanobacteria from stromatolites (ancient, layered, calcium carbonate deposits) off the coast of Western Australia.6 Aside from other wavelengths, this pigment, named chlorophyll f 4.2

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  The Chemistry of Plants

  Perfumes, Pigments and Poisons

  • Margareta Sequin(Author)
  • 2015(Publication Date)
  • Royal Society of Chemistry

    (Publisher)

  Figure 1.26 ). Anthocyanins and betalains, and also tannins and flavones, have numerous OH groups in their molecules that can easily form hydrogen bonds with water. In addition, some of their OH groups are bonded to sugars, making them glycosides. Therefore, these pigments are soluble in water. In contrast, pigments like chlorophyll and carotenes that have no (or very few) OH groups do not dissolve in water, but are fat-soluble. They are stored in their own cell organelles: chlorophyll in chloroplasts and carotenes in chromoplasts.

  The colors of plants that we see are the result of mixtures of pigments. One of the pigments may be dominant, like chlorophyll in green leaves. Structural colors, caused by plant structures like a rough surface or fine hairs on leaves, can contribute to the color shade of a plant part. But they are not as dominant in plants as, for example, in bird feathers or in wings of butterflies where structural colors create many of the colors that we see there.4

  For further illustration of plant pigments, Box 4.1 takes a combined look at plant scents and pigments as attractants of pollinators, whereas Box 4.2 reflects on the pigments in fall coloration.

  Let us explore now the different families of plant pigments and learn about their special characteristics.

  4.2 THE CHLOROPHYLLS

  In Chapter 1 , we encountered chlorophyll a , the main photosynthetic pigment (Figure 1.29 , 1.1 ). There are other types of chlorophylls that distinguish themselves by slight variations in their molecular structures (Figure 4.2 ). All chlorophylls have porphyrin rings, with long sequences of conjugated double bonds, and with a magnesium atom in the center of the ring. The differences are in some of the side chains attached to the porphyrin ring. (R and R′ in Figure 4.2 point out the sites where the differences are.) These variations lead to the absorption of different wavelengths of light—and to a slightly different color of the pigment. A side chain that adds an additional double bond in the conjugated bond pattern enhances absorption of light towards longer wavelengths. Note that chlorophyll b (Figure 4.2 , 4.1 ) has an aldehyde (or CHO) group replacing one of the methyl (CH3 ) groups. The aldehyde group, with a double bond between the carbon and oxygen, is written out for clarity in the figure. If you check the absorption spectra in Figure 1.31 , you can compare the wavelengths of maximum absorption for chlorophyll a and b . Note that in chlorophyll b they are shifted towards longer wavelengths. Chlorophyll b serves as an accessory pigment in green plants as it broadens the range of light that is available for photosynthesis. Other chlorophylls and related pigments are found in algae or in cyanobacteria. Pigments of photosynthesizing organisms that live in water need to be able to make use of light energy that is available in their environment. Quite recently, researchers discovered a new type of chlorophyll in cyanobacteria from stromatolites (ancient layered calcium carbonate deposits), off the coast of Western Australia.5 Aside from other wavelengths, this pigment, named chlorophyll f , 4.2

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  Photophysiology

  Current Topics

  • Arthur C. Giese(Author)
  • 2013(Publication Date)
  • Academic Press

    (Publisher)

  2. Systems which can interact with and quench photosensitizer triplet states. 3. Systems which can serve as preferred substrates for photosensitized oxidations. 4. Systems which can stabilize membranes or repair damaged mem-branes. These mechanisms have been diagrammed schematically in Fig. 19, which shows how a hypothetical cell could protect itself. (1) As has been discussed in Section 2.4.2 of this chapter, there are carotenoid-deficient organisms whose aerobic photosensitivity can be overcome by placing a filter made of carotenoid pigments between the cells and the source of light. This suggests that the pigments are serving as protective filters when present, screening out the potentially harmful radiation (Goldstrohm and Lilly, 1965). (2) The presence of material capable of quenching the triplet state of such endogenous photosensitizers as chlorophyll is essential if cells con-taining such photosensitizers are to continue functioning. The problem of how a photosynthetic cell handles excess radiation has been discussed by Gaffron (1963), among others, who pointed out that a mechanism involving carotenoid pigments capable of inactivating Chi 1 would ex-plain the presence of carotenoid pigments in the obligate photosynthetic bacteria. A mechanism for this phenomenon, first described by Fujimori 5. PROTECTIVE FUNCTION OF CAROTENOID PIGMENTS 189 and Livingston (1957), can be inferred from the work of Chessin et ah (1966), who found that Car 1 can be formed from light absorbed by chlorophyll. If Car 1 is transformed to Car g by a process involving the harmless dissipation of the electronic excitation energy, this would offer an escape route for excess excitation energy acquired by photosynthetic cells. (3) Calvin (1955) and Sistrom et al. (1956) suggested that carotenoids could function as protective agents by serving as preferred substrates in photosensitized oxidations.

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  Physicochemical and Environmental Plant Physiology

  • Park S. Nobel(Author)
  • 2009(Publication Date)
  • Academic Press

    (Publisher)

  aData are expressed per 600 chlorophylls and are for representative leaves of green plants (except for the phycobilins) growing at moderate sunlight levels. Photosystems and the light-harvesting antennae are discussed later in this chapter.

  5.3. Excitation Transfers Among Photosynthetic Pigments

  Chlorophyll is at the very heart of the primary events of photosynthesis. It helps convert the sun's radiant energy into chemical free energy that can be stored in various ways. In this section we will represent light absorption, excitation transfer, and the photochemical step as chemical reactions; this will serve as a prelude to a further consideration of certain molecular details of photosynthesis.

  5.3A. Pigments and the Photochemical Reaction

  The first step in photosynthesis is light absorption by one of the pigments. The absorption event (discussed in Chapter 4 , e.g., Section 4.2E) for the various types of Photosynthetic Pigments described in this chapter can be represented as follows:(5.2)

  where the asterisk refers to an excited state of the pigment molecule caused by the absorption of a light quantum, hν. Trap chl indicates a special type of Chl a (e.g., P680 or P700 ) that occurs much less frequently than do the other chlorophylls (see Table 5-1 ); we will consider its important excitation-trapping properties at the end of this section.

  Because the photochemical reactions take place only at the trap chl molecules, the excitations resulting from light absorption by either the accessory pigments or the other Chl a's must be transferred to the trap chl before they can be used for photosynthesis. The relative rarity of trap chl compared with the other Photosynthetic Pigments means that it absorbs only a small fraction of the incident light. In fact, for green plants under natural conditions, over 99% of the photons are absorbed by either the accessory pigments or Chl a. The migration of excitations from the initially excited species to the trap chl—the mechanism for which we will discuss later—can be represented as follows:(5.3) (5.4) In other words, the direction of excitation transfer or migration is from the accessory pigments to Chl a (Eq. 5.3) and from Chl a

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  Energetics of Photosynthesis

  • Govindjee, Unknown Govindjee(Authors)
  • 2012(Publication Date)
  • Academic Press

    (Publisher)

  One of the xanthophylls (fuco-xanthol), present in diatoms and other brown algae, is thought to be bound to protein in vivo. It is generally accepted that most of carotenes are present in PS I and xanthophylls in PS II. 2.1.3. Phycobilins These water-soluble pigments, present in red and blue-green algae, are open-chain tetrapyrroles. There are two kinds of phycobilins: (1) phyco-cyanins, which predominate in the blue-green algae and account for the absorption maxima around 630 nm ; (2) phycoerythrins, which predominate in the red algae, and absorb around 540 nm (see O'hEocha, 1971). Phyco-bilins are mainly associated with PS II, but they are present in PS I as well. A working model for the composition of the two pigment systems in green plants is shown in Fig. 7. 2.1.4. Bacteriochlorophyll The main light-harvesting pigment of photosynthetic bacteria is BChl—it is a tetrahydroporphyrin. BChl a, in organic solvents, has absorption maxima at 360, 590, and 760 nm. In vivo, the absorption is red-shifted and often has two or more maxima. For example, the purple bacterium Chromatium has absorption peaks at 800, 850, and 870 nm due to bulk BChl a. The green bacteria contain Chlorobium Chi, of which there are two kinds, with absorp-tion at 725 and 750 nm ; in addition they contain a small amount of BChl a absorbing at 810 nm (see Olson and Stanton, 1966). Some bacteria, e.g., Rhodopseudomonas viridis, contain BChl b in these, the long-wavelength absorption maximum lies at 1025 nm. 2.2. Light Emission 2.2.1. Fluorescence The Chi a molecule, upon excitation, by direct light absorption, or through the transfer of excitation energy absorbed in any accessory pigment, goes into the first excited singlet state. The potential energy of the molecule in the excited state can be dissipated in several ways (see Fig. 1).

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