Photosynthetic pigment
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A '''photosynthetic pigment''' ('''accessory pigment'''; '''chloroplast pigment'''; '''antenna pigment''') is a [[pigment]] that is present in [[chloroplast]]s or photosynthetic [[bacterium|bacteria]] and captures the [[light]] energy necessary for [[photosynthesis]].
== Plants ==
[[Plant|Green plants]] have five closely-related photosynthetic pigments (in order of increasing polarity):
*[[Carotene]] - an orange pigment
*[[Phaeophytin|Phaeophytin a]]<ref name=phaeophytin>[http://www.fao.org/ag/agn/jecfa-additives/specs/Monograph1/Additive-128.pdf CHLOROPHYLLS], JECFA, 1987</ref> - a gray-brown pigment
*[[Phaeophytin|Phaeophytin b]]<ref name=phaeophytin /> - a yellow-brown pigment
*[[Chlorophyll|Chlorophyll a]] - a yellow-green pigment
*[[Chlorophyll|Chlorophyll b]] - a blue-green pigment
*[[Xanthophyll]] - a yellow pigment
Chlorophyll a is the most common of the six, present in every plant that performs photosynthesis. The reason that there are so many pigments is that each absorbs light more efficiently in a different part of the [[electromagnetic spectrum|spectrum]]. Chlorophyll a absorbs well at a wavelength of about 400-450 nm and at 650-700 nm; chlorophyll b at 450-500 nm and at 600-650 nm. Xanthophyll absorbs well at 400-530 nm. However, none of the pigments absorbs well in the green-yellow region, which is responsible for the abundant green we see in nature.
==Bacteria==
Like plants, the [[cyanobacteria]] use water as an electron donor for photosynthesis and therefore liberate [[oxygen]]; they also use chlorophyll as a pigment. In addition, most cyanobacteria use [[phycobiliprotein]]s, water soluble pigments which occur in the cytoplasm of the chloroplast, to capture light energy and pass it on to the chlorophylls. (Some cyanobacteria, the prochlorophytes, use chlorophyll b instead of phycobilin.) It is thought that the chloroplasts in plants and algae all evolved from cyanobacteria.
Several other groups of bacteria use the [[bacteriochlorophyll]] pigments (similar to the chlorophylls) for photosynthesis. Unlike the cyanobacteria, these bacteria do not produce oxygen; they typically use [[hydrogen sulfide]] rather than water as the electron donor.
Recently, a very different pigment has been found in some marine γ-[[proteobacteria]]: [[proteorhodopsin]]. It is similar to and probably originated from bacteriorhodopsin (see below under archaea).
==Algae==
[[Green algae]], [[red algae]] and [[glaucophyte]]s all use chlorophylls. Red algae and glaucophytes also use [[phycobiliprotein]]s, but green algae do not.
==Archaea==
Photosynthesis in [[archaea]] is quite different from the systems in other domains of life. Photosynthetic archaea (the [[halobacteria]]) use the pigment [[bacteriorhodopsin]] which acts directly as a [[proton pump]] when exposed to light.
== References ==
<references/>
[[Category:Photosynthetic pigments| ]]
[[cs:Fotosyntetický pigment]]
[[nl:Fotosynthetisch pigment]]
[[pl:Barwniki fotosyntetyczne]]
[[pt:Pigmento fotossintético]]