Pigment System Research Articles

Audiological abnormalities in patients with vitiligo.

Accumulating evidence suggests that vitiligo is a systemic disease affecting the entire pigmentary system. To investigate the subclinical abnormalities of melanin-containing cellular elements of the auditory system in patients with vitiligo. We studied the conventional audiometric investigations and brainstem auditory evoked responses (BAERs) of 57 active patients with vitiligo and 50 healthy human subjects. The I, III and V latencies, and I-III, III-V and I-V interpeak latencies (IPL) between the groups were compared. A mild degree of sensorineural hypoacusis was found in eight patients with vitiligo (14%), whereas no controls demonstrated abnormal audiological results (P =0.006). A statistically significant increase in both ears of the third peak latency (P =0.02, P = 0.01, respectively) and IPL I-III (P = 0.04, P = 0.008, respectively), and a significant increase of the fifth peak latency in the right ear (P = 0.04) were found, compared with controls, but no differences were found for other latencies and IPLs. Melanin may play a significant role in the establishment and/or maintenance of the structure and function of the auditory system and may modulate the transduction of the auditory stimuli by the inner ear.

Haut und Haar

Anti-aging medicine is dedicated to the advancement of technology to detect, prevent, and treat aging related disease and to promote research into methods to retard and optimize the aging process. Dermatology offers good basics for rational preventive and therapeutic anti-aging strategies. The role of the skin in anti-aging medicine is not merely that aging is most obvious on the skin, but that the skin is a highly accessible and unique organ that offers unequaled opportunities to the gerontologist for the study of age-related effects. The study of skin aging focuses on two main streams of interest: On one hand, the esthetic problem and its management; on the other, the biological problem of aging in terms of microscopic, biochemical, and molecular changes. Probably the same molecular mechanisms underlying the aging of skin and its appendages, including the pigmentary system, underlie age-dependent degenerative changes of the inner organs and entire organism. The skin and hair are subject to intrinsic or physiologic aging, and extrinsic or premature aging due to external factors. Intrinsic factors are related to individual genetic and epigenetic mechanisms with interindividual variation. Extrinsic factors include ultraviolet radiation and cigarette smoking. Primary prevention encompasses measures that are taken before the aging process has started, secondary prevention when the first signs of aging have come into sight. Eventually, tertiary measures are aimed at correcting established signs of aging. Prevention starts with photoprotection and avoidance of cigarette smoking. In dermatologic practice sun protecting agents, dermocosmetic substances, hair growth promoting agents, and anti-aging compounds play an ever increasing role. Finally, tertiary anti-aging measures include minimally invasive cosmetic procedures such as chemical peels, microdermabrasion, soft tissue fillers, non-ablative laser rejuvenation, radiofrequency techniques and botulinum toxin, as well as laser skin resurfacing and corrective surgical procedures, including autologous hair transplantation.

Photosynthesis and negative entropy production

The widely held view that the maximum efficiency of a photosynthetic pigment system is given by the Carnot cycle expression (1 − T/ T r) for energy transfer from a hot bath (radiation at temperature T r) to a cold bath (pigment system at temperature T) is critically examined and demonstrated to be inaccurate when the entropy changes associated with the microscopic process of photon absorption and photochemistry at the level of single photosystems are considered. This is because entropy losses due to excited state generation and relaxation are extremely small (Δ S ≪ T/ T r) and are essentially associated with the absorption-fluorescence Stokes shift. Total entropy changes associated with primary photochemistry for single photosystems are shown to depend critically on the thermodynamic efficiency of the process. This principle is applied to the case of primary photochemistry of the isolated core of higher plant photosystem I and photosystem II, which are demonstrated to have maximal thermodynamic efficiencies of ξ > 0.98 and ξ > 0.92 respectively, and which, in principle, function with negative entropy production. It is demonstrated that for the case of ξ > (1 − T/ T r) entropy production is always negative and only becomes positive when ξ < (1 − T/ T r).

Pigmentação testicular em Physalaemus nattereri (Steindachner) (Amphibia, Anura) com observações anatômicas sobre o sistema pigmentar extracutâneo

O presente estudo foi realizado com o intuito de relatar a ocorrência e morfologia de células pigmentares viscerais constituintes do "sistema pigmentar extracutâneo" em Physalaemus nattereri (Steindachner, 1863) (Leptodactylidae). Foram utilizados dez exemplares machos para a análise macroscópica e obtenção de fragmentos testiculares incluídos em resina e corados com H/E. Os anuros, dentre outros animais exotérmicos, possuem células especiais, os melanócitos, que se caracteriza por intensa pigmentação e sintetiza melanina, além de melanomacrófagos, que se caracteriza por atividade fagocítica e muitas vezes apresentam intensa pigmentação. A nomenclatura destas células não é consensual e, por isso, várias denominações são apresentadas, principalmente nos seguintes órgãos: fígado (como sinônimo de células de Kupffer), rins, baço e menos freqüentemente em outras localizações, com os termos - células pigmentares, células pigmentares extracutâneas, macrófagos pigmentados, melanomacrófagos, melanófagos, melanóforos e melanócitos. Para os anuros os estudos são recentes e relatam células pigmentares em poucas espécies. Em Physalaemus nattereri e alguns anuros, os pigmentos melânicos são encontrados, além da cútis, em outros órgãos constituindo um sistema pigmentar extracutâneo, com diferentes ocorrências, tipos e quantidade em distintas espécies. Associados ao aparelho reprodutor de P. nattereri, os melanócitos foram observados nas gônadas, na albugínea e no interstício, especialmente associado com vasos sangüíneos. A notória presença de numerosas células com pigmento distribuídas no testículo confere uma coloração que varia do preto mesclado com branco ao preto intenso. Trata-se de uma rara peculiaridade e não há informações sobre seu significado funcional ou valor biológico.

Evaluation of zinc phosphate and zinc chromate effectiveness via AC and DC methods

This research is based on studying corrosion inhibitive effect of two anticorrosive pigments, zinc phosphate and zinc chromate. AC or electrochemical impedance spectroscopy (EIS) and linear sweep voltammetry (polarization) have been examined. At the first step, the pigments effects on electrochemical behavior of mild steel as bare metal have been studied in the presence of 3.5% (w/w) NaCl when saturated solutions of the pigments were prepared. At the second step, the pigments were dispersed in the epoxy resin. Electrochemical impedance spectroscopy of epoxy coated mild steel has been investigated when they were immersed in 3.5% (w/w) NaCl solutions. Coated mild steel at the same λ ( λ is the pigment volume concentration to critical pigment volume concentration ratio) has been fitted for both pigmented systems with porous film model. The first and second steps comparison showed different mechanisms for the zinc phosphate when they were used in the solution and coating.

Pigmentation disorders in Taiwanese skin: a clinical experience

Pigmentation disorders in Taiwanese skin: a clinical experience

Histological variation of Japanese skin with aging

Histological variation of Japanese skin with aging

Effect of red and far-red light on inhibition of hypocotyl elongation in ecotypes of Betula pendula Roth

Plants sense the quality, quantity, and duration of light signals and use them to optimise their growth and development. These signals are perceived by special light receptors of which the phytochrome pigment system is one of the most important for photomorphogenetic responses. Using special diodes that emit monochromatic light, we studied the effect of red (R), far-red (FR) and R+FR combinations on hypocotyl elongation of latitudinal ecotypes of Betula pendula . Continuous R and FR inhibited hypocotyl elongation equally, but inhibition was higher when seedlings were irradiated by continuous R+FR. In all cases, inhibition increased with increasing irradiance, from 0.75 μmol m -2 s -1 to 76 μmol m -2 s -1 . Moreover, seedlings treated by R or R+FR synthesised more anthocyanins than those exposed to FR. Accumulation of anthocynins increased with increasing irradiance up to about 19 μmol m -2 s -1 . Key Words: Anthocyanin, diode, ecotype, monochromatic, photomorphogenesis, photosynthetically active radiation, skotomorphogenesis. African Journal of Biotechnology Vol.4(1) 2005: 50-56

CHARACTERIZATION OF TESTUDINE MELANOMACROPHAGE LINEAR, MEMBRANE EXTENSION PROCESSES—CABLEPODIA—BY PHASE AND ATOMIC FORCE MICROSCOPY

Melanomacrophages (MMs) are a component of an internal, pigmented cell system in liver and splenic tissues of some fishes, anurans, and reptiles. The cells have been found in centers or aggregates in sinusoids and are associated with cells capable of producing a peptide cytokine and immunoglobulins. A unique cell extension process has been observed in turtle MMs placed into cell culture, and this process has been studied by light and atomic force microscopy. These structures, referred to as cablepodia, are uniquely straight, narrow, and unbranching and appear to originate from growth cones opposite lamellipodia. Cablepodia were found to connect with other turtle MMs and fibroblasts forming cell networks. Dividing fibroblasts to which a cablepodium attached ceased cell division. The observations collectively suggest that a principal reason for aggregations of MMs in internal organs of lower vertebrates is their ability to form interconnected networks of cell processes for trapping and processing of particulate matter, cells, and infectious organisms and, possibly, for the communication of cell signals and transfer of intracellular materials.

Evaluation of a spinel based pigment system as a CO oxidation catalyst

Commercially available black pigment consisting of mixed manganese, copper and iron oxides was tested as a catalyst as well as an oxidant for CO oxidation. The crystalline structures of the catalyst were determined by XRD as Cu1.5Mn1.5O4 mixed with Fe2O3 and Mn3O4 oxides. The fresh catalyst with 30–300nm size and a BET surface area of 18.5m2g−1 was able to completely convert CO at 525°C even at a significantly high COO2He gas flow rate of 1000mlmin−1 (corresponding space velocity being ∼310,000h−1). While the reaction rate was independent of oxygen concentration in the range tested (0.8–9.9vol.% of O2 at a constant CO concentration of 0.85%), it depended on CO concentration. The reaction order over fresh catalyst was measured to be 0.85 with respect to CO with an activation energy value of 47.9kJmol−1. Application of a reduction followed by oxidation type of heat treatment on fresh catalyst induced the formation of fine clusters or domains of ∼5nm on the surface of the catalyst particles. This refined morphology with high density of defects led to a great improvement in catalytic activity. Complete CO conversion was achieved at 180°C over a heat treated catalyst. This change in morphology also led to higher reducibility of mixed oxide system after heat treatment as indicated by TPR results. The mixed oxides of transition metals can be a viable alternative to precious metal and noble metal containing catalysts for oxidation of CO.

Toxic effects of isoproturon on periphyton communities – a microcosm study

Coastal and estuarine ecosystems are increasingly exposed to herbicide contamination. To study the potential risks of these pollutants, the establishment of periphyton communities under exposure of a concentration series of isoproturon in a range of 0.0024–0.312 mg L −1 was investigated in a microcosm study. After two weeks of growth, chronic effects on biomass development, measured as Chl a fluorescence, taxonomic composition and photosynthetic capacity of PS II of attached microalgae were analysed using a pulse-amplitude modulated (PAM) fluorescence-based method. Algal classes were differentiated according to their pigment systems using four excitation wavelengths. Biomass remained constant up to pre-exposure concentrations of 0.02 mg L −1 isoproturon but decreased within one order of magnitude at the highest test concentration. Algal classes shifted from diatoms to chlorophytes at pre-exposure concentrations of 0.02–0.39 mg L −1. Community structure of diatoms representing the dominant group of attached algae at lower test concentrations was studied by microscopic analysis revealing that species numbers were highest at lowest test concentrations as compared to controls. At higher test concentrations Navicula halophila dominated with 89% of the diatom biomass but was abnormally shaped. Pollution-induced community tolerance (PICT) of periphyton to isoproturon was determined by short-term inhibition tests of photosynthesis. Pre-exposed communities increased their effect concentrations (EC 50) up to threefold within the 0.039 mg L −1 pre-treatment. Our results suggest that attached microalgal communities have a high potential of tolerance development to isoproturon at lower levels of contamination due to the replacement of sensitive species by more tolerant algae, although these species seemed to be affected too. We conclude that herbicide concentrations in river basins, estuaries or coastal zones may change community structure and primary production of microphytobenthos even when the contamination does not exceed levels of acute toxicity.

Visual pigment composition in zebrafish: Evidence for a rhodopsin–porphyropsin interchange system

Numerous reports have concluded that zebrafish (Danio rerio) possesses A1-based visual pigments in their rod and cone photoreceptors. In the present study, we investigated the possibility that zebrafish have a paired visual pigment system. We measured the spectral absorption characteristics of photoreceptors from zebrafish maintained in different temperature regimes and those treated with exogenous thyroid hormone using CCD-based microspectrophotometry. Rods from fish housed at 15 degrees C and 28 degrees C were not significantly different, having lambda max values of 503 +/- 5 nm (n = 106) and 504 +/- 6 nm (n = 88), respectively. Thyroid hormone treatment (held at 28 degrees C), however, significantly shifted the lambda max of rods from 503 +/- 5 nm (n = 194) to 527 +/- 8 nm (n = 212). Cone photoreceptors in fish housed at 28 degrees C (without thyroid hormone treatment) had lambda max values of 361 +/- 3 nm (n = 2) for ultraviolet-, 411 +/- 5 nm (n = 18) for short-, 482 +/- 6 nm (n = 9) for medium-, and 565 +/- 10 nm (n = 14) for long-wavelength sensitive cones. Thyroid hormone treatment of fish held at 28 degrees C significantly shifted the lambda max of long-wavelength sensitive cones to 613 +/- 11 nm (n = 20), substantially beyond that of the lambda max of the longest possible A1-based visual pigment (approximately 580 nm). Thyroid hormone treatment produced smaller shifts of lambda max in other cone types and increased the half-band width. All shifts in photoreceptor lambda max values resulting from thyroid hormone treatment matched predictions for an A1- to A2-based visual pigment system. We therefore conclude that zebrafish possess a rhodopsin-porphyropsin interchange system that functions to spectrally tune rod and cone photoreceptors. We believe that these observations should be carefully considered during analysis of zebrafish spectral sensitivity.

Effect of wood ash application on the biomass distribution and physiological state of Norway spruce seedlings on sandy soils

The effect of wood ash applied as a fertiliser (0.25, 0.5 and 1 kg m−2) to nutrient poor sandy soil on 4-year-old Norway spruce (Picea abies) growing in small-scale sample plots was studied. Analyses carried out with roots, stems, needles and shoots of different age showed that an increase in the pH level and K and Ca concentrations and a decrease in N and P concentrations in the soil was accompanied by a disbalance of nutrients in tree compartments. Stimulation of pigment synthesis in Norway spruce needles was observed, and no disbalances occurred in the pigment system (Chl a/Chl b, TChl/Car) guaranteeing normal process of photosynthesis. Biomass responses to wood ash application depended on the age of needles and shoots, being only slightly notable in current year organs. Inhibition of height growth of seedlings, but stimulation of root biomass was established.

Photoperiodic Regulationof Apical Growth Cessation in Northern Tree Species

Summary Tree species adapted to the climatic conditions of the northern boreal and subarctic vegetation zones have a capacity to develop a very high level of frost hardiness, even to survive the temperature of liquid nitrogen in midwinter. Proper timing of hardening, as well as of dehardening, is crucial for winter survival of these species. In northern tree species, cessation of apical elongation growth and bud set is a prerequisite for developmental and metabolic processes leading to hardening, and this chain of events is induced by photoperiod. The northern tree species are closely adapted to the local light climate and display photoperiodic ecotypes. The critical photoperiod is under genetic control and increases with increasing latitude of origin of the eco-type. The photoperiod is probably perceived by the phytochrome system, but the role of other pigment systems, like cryptochrome, has not been studied in woody plants. Phytochrome genes have been cloned from both conifers and deciduous species, but so far we do not have any information about possible differences between photoperiodic ecotypes at the phytochrome level. Northern and southern ecotypes have different responses to red:far red ratios, which could indicate differences in composition of their phytochrome systems, for example, the proportions of phytochrome A and B. Both phytochrome A and phytochrome B can be involved in photoperiodic responses. Experiments with transgenic hybrid aspen suggest that responses to photoperiod could be affected by the amount of phytochrome A present in plants. In deciduous species, the plant hormone gibberellin A1 (GA1) can completely substitute for a long photoperiod, and short day induced cessation of growth is preceded by a significant reduction of GA1 levels, particularly in the elongation zone. Photoperiodic control of GA metabolism is supported by several studies, but very little is known about the interaction between phytochrome and GA metabolism and/or responsiveness to GA1. Although our knowledge is still very fragmentary, available results suggest that cessation of growth and initiation of hardening in trees can be controlled both through the phytochrome and the GA mediated systems. Research with tree species is a tedious and slow process, but with the emerging new methods and approaches, we may expect exciting new results in the near future.

A study of molecular interactions in light-harvesting complexes LHCIIb, CP29, CP26 and CP24 by Stark effect spectroscopy

Electric field-induced absorption changes (electrochromism or Stark effect) of the light-harvesting PSII pigment–protein complexes LHCIIb, CP29, CP26 and CP24 were investigated. The results indicate the lack of strong intermolecular interactions in the chlorophyll a (Chl a) pools of all complexes. Characteristic features occur in the electronic spectrum of Chl b, which reflect the increased values of dipole moment and polarizability differences between the ground and excited states of interacting pigment systems. The strong Stark signal recorded for LHCIIb at 650–655 nm is much weaker in CP29, where it is replaced by a unique Stark band at 639 nm. Electrochromism of Chl b in CP26 and CP24 is significantly weaker but increased electrochromic parameters were also noticed for the Chl b transition at 650 nm. The spectra in the blue region are dominated by xanthophylls. The differences in Stark spectra of Chl b are linked to differences in pigment content and organization in individual complexes and point to the possibility of electron exchange interactions between energetically similar and closely spaced Chl b molecules.

The influence of substrate absorbency on coating surface energy

The surface energy of coating layers influences their final properties such as their ability to repel or absorb fluids. Recent work has shown that the substrate, due to absorption, can alter the surface chemistry of the top coating layer. However, the influence of substrate properties on coating surface energies is not reported in the literature. Three coatings, based on a pigment and a latex binder, are applied on three different substrates that differ in terms of absorption properties. The three coatings were also modified with a soluble polymer. Contact angle measurements of three different probe fluids were measured. These contact angles were used to estimate the polar, dispersive, and total surface energy of the coating layers. Surface energies were also determined for the latex and pigments. The contact angles and surface energies of the latex films and pigments agree with the expected results. Most of the results for the coating layers agree with the reported surface chemistry of these coatings. Large pigment systems on absorbent substrates have a high contact angle and low surface energy. These results agree with the expected results based on the surface chemistry reported in past work. The results for the fine pigment system had low contact angles and high surface energies and did not agree with the expected results. The contact angles may be influenced by the surface roughness of the coatings or the expected surface energy of a heterogeneous surface may not be a simple function of the surface composition.

The color loci of mice--a genetic century.

Color loci in mammals are those genetic loci in which mutations can affect pigmentation of the hair, skin, and/or eyes. In the mouse, over 800 phenotypic alleles are now known, at 127 identified color loci. As the number of color loci passed 100 only recently, we celebrate this 'century' with an overview of these loci, especially the 59 that have been cloned and sequenced. These fall into a number of functional groups representing melanocyte development and differentiation, melanosomal components, organelle biogenesis, organelle transport, control of pigment-type switching, and some systemic effects. A human ortholog has been identified in all cases, and the majority of these human genes are found to be loci for human disorders, often affecting other body systems as well as pigmentation. We expect that a significant number of color loci remain to be identified. Nonetheless, the large number known already provide a treasury of resources for reconstruction of the mechanisms, at the subcellular, cellular and tissue levels, that produce a functional pigmentary system and contribute to the normal development and functioning of many other organ systems. The mutant mice also provide valuable models for the study of human disease.

Studying insect photoperiodism and rhythmicity: Components, approaches and lessons

Components of daily and seasonal timing systems in insects are reviewed. Photoperiod indicates seasonal position reliably, but signals can be much modified by habitat, latitude and season. Several receptor features and pigment systems are known, with different daily, seasonal and general functions, including differences between circadian and seasonal reception. Clocks can serve several different purposes, functioning as daily oscillators, interval timers or through successive requirements. The molecular functioning of circadian clocks is best known, but even so there is considerable complexity and diversity and much remains to be discovered. We know relatively little about the internal states that provide information for timed responses (such as the photoperiodic counter), about the central controlling mechanism, or about the effectors that transmit output signals. Nevertheless, temporal responses serve a very great range of purposes in insects, and the reported complexity in all of the components of timing systems reflects complex ecological needs across daily and seasonal intervals. The variety of components and the complexity of interactions reported (even within species), as well as the diversity of such elements as photosensitive pigments, molecular clock function and potential neurotransmitters, suggests that - unlike some earlier expectations - there is no single master clock for all timing functions in insects.Insect photoperiodism and rhythmicity have been studied by both observational or direct approaches (examination of system elements or devices, and qualities such as survival), and by inferential or indirect approaches (such as interpretation of various responses to photoperiod, modelling, and estimating fitness). Many students work with only one approach, but the power of different approaches is not equal, and knowledge at one level may not give answers at another. These difficulties tend to limit our understanding of the linkages among components.This overview suggests several lessons for the study of photoperiodism and rhythmicity. There are multiple elements, complex integration and a diversity of clocks, showing that different processes serve different purposes. The diversity of findings also results from the fact that different investigative approaches, which depend on the question being asked and on the perspective of the investigator, can influence the outcome of the investigation. Given these complexities, I believe that the key to interpreting photoperiodic and circadian responses is their ecological value. Notwithstanding the interest of timing mechanisms or their parts and of specific responses, daily rhythms and seasonal timing are best understood through the essential context provided by the ecological demands on the actual organisms under study.

Inhibitor pretreatment synergies demonstrated using a scanning Kelvin probe technique

A scanning Kelvin probe technique has been used to study the influence of pretreatment and pigment interaction on the kinetics and mechanism of corrosion driven delamination processes affecting model polyvinyl butyral coatings adherent to the intact zinc surface of hot dip galvanised steel. The effects of incorporating dispersions of strontium chromate (SrCrO4), silica and bentonite based Cerium (III) cation exchange pigments within the polyvinyl butyral coating are investigated on galvanised steel specimens in the absence and presence of a mixed oxide/chromate rinse surface pretreatment. Placing aqueous sodium chloride electrolyte onto a penetrative coating defect establishes an electrochemical delamination cell in which cathodic O2 reduction at the delamination front is coupled to anodic zinc dissolution at the coating defect by a thin layer of electrolyte which ingresses beneath the delaminated polyvinyl butyral film. The SrCrO4 pigmented polyvinyl butyral films allow CrO42- diffusion directly into the underfilm electrolyte layer and profoundly inhibit delamination both in the presence and absence of pretreatment. Without pretreatment delamination is progressively retarded by increasing SrCrO4 pigment volume fraction. The addition of the pretreatment decreases the delamination rate in all cases by around between 20 and 50%, probably through improved adhesion to the metal substrate. In contrast, polyvinyl butyral films containing dispersed cerium exchanged bentonite clay (CEB) and cerium exchanged Shieldex (CES) pigments do not efficiently inhibit delamination in the absence of the mixed oxide pretreatment. In the presence of pigment volume fractions of up to 0.15, the delamination rate is only decreased to ~20% of its original value. However, when used in conjunction with a pretreated surface, both CEB and CES pigments profoundly inhibit corrosion driven delamination, with observed rates reduced to levels below those measured for the SrCrO4 pigmented system. Thus there appears to be a synergy between the CEB and CES pigments and the mixed oxide (chromate rinse) pretreatment. This synergy is believed to be related either to the ease with which a cerium hydr(oxide) inhibition film can form on the oxide covered surface of the pretreated material, or to the underfilm interaction of pigment derived cathodic (Ce3+) and pretreatment derived anodic (CrO42-) inhibitors.

PHOTOSYNTHETIC PIGMENT COMPOSITION IN THE PRIMITIVE GREEN ALGA MESOSTIGMA VIRIDE (PRASINOPHYCEAE): PHYLOGENETIC AND EVOLUTIONARY IMPLICATIONS1

The photosynthetic pigment composition of Mesostigma viride Lauterborn, a primitive green alga, was determined. This alga contained chl a and b, lycopene, lutein, siphonaxanthin, γ‐carotene, β‐carotene, antheraxanthin, violaxanthin, neoxanthin, and two novel carotenoid fatty acid esters, siphonaxanthin C12:0 ester and siphonaxanthin C14:0 ester. The esters were saturated, whereas all previously identified siphonaxanthin and loroxanthin esters have been mono‐unsaturated (trans‐Δ2). Neoxanthin was the all‐trans form. This is the first such case detected in the chloroplasts of green plants. The 9′‐cis form of neoxanthin is believed to be universally present in the chloroplasts of green plants (Streptophyta and Chlorophyta) and is a precursor of abscisic acid. However, the 9′‐cis form was not found in M. viride. Based on these results, we discuss the phylogenetic implications and early evolution of the antenna pigment system in green plants.