Functions Of Carotenoids In Photosynthesis Research Articles

Carotenoids in algae: distributions, biosyntheses and functions.

For photosynthesis, phototrophic organisms necessarily synthesize not only chlorophylls but also carotenoids. Many kinds of carotenoids are found in algae and, recently, taxonomic studies of algae have been developed. In this review, the relationship between the distribution of carotenoids and the phylogeny of oxygenic phototrophs in sea and fresh water, including cyanobacteria, red algae, brown algae and green algae, is summarized. These phototrophs contain division- or class-specific carotenoids, such as fucoxanthin, peridinin and siphonaxanthin. The distribution of α-carotene and its derivatives, such as lutein, loroxanthin and siphonaxanthin, are limited to divisions of Rhodophyta (macrophytic type), Cryptophyta, Euglenophyta, Chlorarachniophyta and Chlorophyta. In addition, carotenogenesis pathways are discussed based on the chemical structures of carotenoids and known characteristics of carotenogenesis enzymes in other organisms; genes and enzymes for carotenogenesis in algae are not yet known. Most carotenoids bind to membrane-bound pigment-protein complexes, such as reaction center, light-harvesting and cytochrome b6f complexes. Water-soluble peridinin-chlorophyll a-protein (PCP) and orange carotenoid protein (OCP) are also established. Some functions of carotenoids in photosynthesis are also briefly summarized.

Ultrafast transient absorption spectroscopy: principles and application to photosynthetic systems

The photophysical and photochemical reactions, after light absorption by a photosynthetic pigment–protein complex, are among the fastest events in biology, taking place on timescales ranging from tens of femtoseconds to a few nanoseconds. The advent of ultrafast laser systems that produce pulses with femtosecond duration opened up a new area of research and enabled investigation of these photophysical and photochemical reactions in real time. Here, we provide a basic description of the ultrafast transient absorption technique, the laser and wavelength-conversion equipment, the transient absorption setup, and the collection of transient absorption data. Recent applications of ultrafast transient absorption spectroscopy on systems with increasing degree of complexity, from biomimetic light-harvesting systems to natural light-harvesting antennas, are presented. In particular, we will discuss, in this educational review, how a molecular understanding of the light-harvesting and photoprotective functions of carotenoids in photosynthesis is accomplished through the application of ultrafast transient absorption spectroscopy.

Effect of solvent on absorption spectra of all-trans-β-carotene under high pressure

The absorption spectra of all-trans-beta-carotene in n-hexane and carbon disulfide (CS(2)) solutions are measured under high pressure at ambient temperature. The common redshift and broadening in the spectra are observed. Simulation of the absorption spectra was performed by using the time-domain formula of the stochastic model. The pressure dependence of the 0-0 band wavenumber is in agreement with the Bayliss theory at pressure higher than 0.2 GPa. The deviation of the linearity at lower pressure is ascribed to the reorientation of the solvent molecules. Both the redshift and broadening are stronger in CS(2) than that in n-hexane because of the more sensitive pressure dependence of dispersive interactions in CS(2) solution. The effect of pressure on the transition moment is explained with the aid of a simple model involving the relative dimension, location, and orientation of the solute and solvent molecules. The implication of these results for light-harvesting functions of carotenoids in photosynthesis is also discussed.

Redox functions of carotenoids in photosynthesis.

Carotenoids are well-known as light-harvesting pigments. They also play important roles in protecting the photosynthetic apparatus from damaging reactions of chlorophyll triplet states and singlet oxygen in both plant and bacterial photosynthesis. Recently, it has been found that beta-carotene functions as a redox intermediate in the secondary pathways of electron transfer within photosystem II and that carotenoid cation radicals are transiently formed after photoexcitation of bacterial light-harvesting complexes. The redox role of beta-carotene in photosystem II is unique among photosynthetic reaction centers and stems from the very strongly oxidizing intermediates that form in the process of water oxidation. Because of the extended pi-electron-conjugated system of carotenoid molecules, the cation radical is delocalized. This enables beta-carotene to function as a "molecular wire", whereby the centrally located oxidizing species is shuttled to peripheral redox centers of photosystem II where it can be dissipated without damaging the system. The physiological significance of carotenoid cation radical formation in bacterial light-harvesting complexes is not yet clear, but may provide a novel mechanism for excitation energy dissipation as a means of photoprotection. In this paper, the redox reactions of carotenoids in photosystem II and bacterial light-harvesting complexes are presented and the possible roles of carotenoid cation radicals in photoprotection are discussed.

How carotenoids protect bacterial photosynthesis.

The essential function of carotenoids in photosynthesis is to act as photoprotective agents, preventing chlorophylls and bacteriochlorophylls from sensitizing harmful photodestructive reactions in the presence of oxygen. Based upon recent structural studies on reaction centres and antenna complexes from purple photosynthetic bacteria, the detailed organization of the carotenoids is described. Then with specific reference to bacterial antenna complexes the details of the photoprotective role, triplet triplet energy transfer, are presented.

Vibrational Relaxation and Redistribution in the 2Ag- State of all-trans-Lycopene As Revealed by Picosecond Time-Resolved Absorption Spectroscopy

Vibrational relaxation in the 2Ag- (S1) state of all-trans-lycopene, which takes place in a time scale slower than that of internal conversion, has been found by picosecond time-resolved absorption spectroscopy: The time-resolved Sn (2Bu+) ← S1 (2Ag-) absorption spectra of this carotenoid in quinoline and CS2 solutions can be explained in terms of vibrational structures originating from the CC (ν1) and C−C (ν2) stretching modes, and the time scales of vibrational relaxation (kν1 and kν2 defined for the lowest vibrational transition) relative to that of internal conversion (k) are estimated by spectral simulation; the values of kν1/k and kν2/k are around 0.6 and 0.3 in the quinoline solution and 0.2 and 1.6 in the CS2 solution. The slower vibrational relaxations are discussed in light of the light-harvesting function of carotenoids in photosynthesis.

Structures and Functions of Carotenoids in Photosynthesis

Structures and Functions of Carotenoids in Photosynthesis

Carotenoids as accessory light-harvesting pigments

Abstract

Mimicry of antenna and photo-protective carotenoid functions by a synthetic carotenoporphyrin

Carotenoid pigments, ubiquitous in photosynthetic membranes, are essential for the survival of green plants1. Two facets of carotenoid function are recognized in photosynthetic membranes. First, carotenoids prevent the chlorophyll-photosensitized formation of highly destructive singlet oxygen by intercepting the chlorophyll triplet states2–10 and may also scavenge additional singlet oxygen present11,12. Second, carotenoids perform an antenna function by transferring the energy of absorbed light at the singlet excited state level to the chlorophyll system for the execution of photosynthetic work13–16. Nevertheless, the mechanisms by which carotenoids perform these functions are poorly understood. We now report that a unique synthetic carotenoporphyrin I consisting of a carotenoid part covalently linked to a synthetic tetraarylporphyrin successfully mimics both the photophysical functions of carotenoids in photosynthesis. The explanation for this seems to be the close interaction of the carotenoid and porphyrin π-electron systems.

THE MECHANISM OF SINGLET‐SINGLET EXCITATION ENERGY TRANSFER FROM CAROTENOIDS TO CHLOROPHYLL

Abstract— It is proposed that the light‐harvesting function of carotenoids in photosynthesis requires electron exchange between the energy donor (carotenoids) and the acceptor (antenna Chi molecules); this supports an earlier suggestion by Goedheer (1972) that there exists a close spatial relationship between these pigments in vivo.

Function of Carotenoids in Photosynthesis

Function of Carotenoids in Photosynthesis

Function of carotenoids in photosynthesis.

Function of carotenoids in photosynthesis.