Pigments accessory

Chlorophyll b occurs as an accessory pigment of the light-harvesting systems in land plants and green algae, and comprises one-third (or less) of total chlorophyll. The biosynthesis of chlorophyll b has been an area of active research particularly regarding its compartmentalization in chloroplast membranes, identification of the gene for chlorophyllide a oxidase, and characterization of the enzymes involved. ... 

Carotenoids protect photosynthetic organisms against potentially harmful photooxidative processes and are essential structural components of the photosynthetic antenna and reaction center complexes. Plant carotenoids play fundamental roles as accessory pigments for photosynthesis, as protection against photooxidation, and... 

Since the function of most of the chlorophyll and the accessory pigments is thought to be the harvesting of light, one would expect the action spectrum... 

When the trap light is utilized predominantly by photosystem II (e.g., by irradiation of 563 nm, which is absorbed by the main accessory pigment C-phycoerythrin),... 

Figure 10.16 Solar energy transfer from accessory pigments to the reaction centre, (a) The photon absorption by a component of the antenna complex transfers to a reaction centre chlorophyll, or, less frequently, is reemitted as fluorescence, (b) The electron ends up on the reaction centre chlorophyll because its lowest excited state has a lower energy than that of the other antenna pigment molecules. (From Voet and Voet, 2004. Reproduced with permission from John Wiley Sons., Inc.)...

As mentioned in Sect. 13.3.6, carotenoids serve mainly as accessory pigments in the light harvesting complexes of the photosynthetic apparatus, and additionally as cellular protection against ROS. Whether carotenoids also act as passive UV-sunscreens is... 

The sunlight is absorbed by a number of pigments, of which chlorophyll a is the most important. The absorption spectrum of chlorophyll a is shown in Fig. 10.3. Apart from chlorophyll a there are accessory pigments which function as lightharvesting antennae and transfer the energy to the chlorophyll a. This is an elegant way to efficiently collect sunlight. 

Trees, C.C., D.K. Clark, R.R. Bidigare, and M.E. Ondrusek. 2000. Chlorophyll a versus accessory pigment concentrations within the euphotic zone A ubiquitous relationship Limnology and Oceanography 45 1130-1143. 

Carotenoids Organic molecules that function as accessory pigments in phytoplankton photosynthesis. 

Carotene (a carotenoid) and (d) lutein (a xanthophyll) are accessory pigments in plants. The areas shaded pink are the conjugated systems (alternating single and double bonds) that largely account for the absorption of visible light. 

FIGURE 19-42 A light-harvesting complex, LHCII. The functional unit is an LHC trimer, with 36 chlorophyll and 6 lutein molecules. Shown here is a monomer, viewed in the plane of the membrane, with its three transmembrane a-helical segments, seven chlorophyll a molecules (green), five chlorophyll b molecules (red), and two molecules of the accessory pigment lutein (yellow), which form an internal cross-brace. 

Accessory Pigments Extend the Range of Light Absorption... 

FIGURE 19-45 Organization of photosystems in the thylakoid membrane. Photosystems are tightly packed in the thylakoid membrane, with several hundred antenna chlorophylls and accessory pigments surrounding a photoreaction center. Absorption of a photon by any of the antenna chlorophylls leads to excitation of the reaction center by exciton transfer (black arrow). Also embedded in the thylakoid membrane are the cytochrome bkf complex and ATP synthase (see Fig. 19-52). 

PHYCOCHRYSIN A golden brown accessory pigment which overlies the other pigments in the Chrysophyceae or chrysochrome. 

The carotenes and carotenoids are very important accessory pigments (Fig. 23-22). The major component in most green plants is (3-carotene. Green sulfur bacteria contain y-carotene in which one end of the molecule has not undergone cyclization and resembles lycopene (Fig. 22-5). Chloroplasts also contain a large variety of oxygenated carotenoids (xanthophylls). Of these, neoxanthin, violaxanthin... 

Figure 23-22 Absorption spectra of chlorophylls and accessory pigments compared. Redrawn from G. and R. Govindjee,265 and from J. J. Wolken 266...

A third class of accessory pigment of more limited distribution are the open tetrapyrroles, sometimes called "plant bile pigments" because of their relationship to the pigments of animal bile (Fig. 24-24). 

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