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PHYCOLOGICAL SOCIETY OF AMERICA

Botryoglossum Photosynthetic Pigments 

Morphology     Ecology     Life History     Taxonomy     Reproduction 

Photosynthesis

This is the process by which most autotrophs produce their food,  using the Sun. This simple chemical reaction utilizing the Sun's energy produces food energy for all the world's inhabitants in the form of the sugar glucose, not to mention most of the oxygen animals need to breathe. The simple chemical equation is:

Sunlight + CO₂ + H₂O = C₆H₁₂O₆ + O₂

Algae's ability to trap light and convert it to energy for this reaction stems from photosynthetic pigments. The most ubiquitous pigments, those used in all photosynthetic reactions in the plant and other kingdoms, are the chlorophylls. Red algae use chlorophyll a to make the conversion of the photons from sunlight into a utilizable energy source.  

Chlorophyll a has a chlorin ring structure with a central magnesium ring structure, shown in the picture, where absorption occurs. There is also a lengthy hydrocarbon "tail" (C₁₉H₃₇) labeled as Phytyl.

Chlorophyll a in and of itself can only absorb certain parts of the spectrum of visible light. If an absorption spectrum is looked at, chlorophyll a is seen to absorb red and violet light, unable to utilize the energy from the middle of the spectrum. This is where accessory pigments come in. 

Accessory pigments absorb the intermediate length light that chlorophyll can't. Red algae use phycobilins and carotenoids for this purpose. Specifically, phycoerythrin and phycocyanin are used to absorb to green and yellow-orange range of light, respectively. Carotenoids, such as betacarotene, also are present to absorb blue light. Together, these pigments can absorb almost the full range of light available to the plant. 

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The accessory pigments absorb photons and pass them off to pigments that can absorb increasingly longer wavelengths until they reach a chlorophyll a molecule in the "reaction center" of this "antennae" of pigments. The chlorophyll then reaches an excited state and takes part in the photosynthetic reaction.

 Phycoerythrin appears as red, as does betacarotene. Along with the blueish color of phycocyanin, these blended pigments create the deep purplish-red color of Botryoglossum. As the phycobilins are water-soluble pigments, when algae dies and remains soaking in the sea, the color begins to soak out of the tissue. This is why you will often find that beach-wrecked specimens are splotchy and pink. 

The depth at which Botryoglossum resides increases the usefulness of these extraneous pigments. As chlorophyll a seems to be more absorptive of blue light than red, and in the deep subtidal the weaker, shorter wavelengths toward the violet end of the spectrum have trouble penetrating the depths, it is advantageous to possess pigments which can make use of any light which actually does filter down. Also, by having the phycobilins, which cluster their absorption toward the longer end of the spectrum, it is more likely that it will be able to use what light there is.

From Life: The Science of Biology. copyright 1998, Sinauer Associates, Inc. p. 171.

The above absorption spectrum shows just how very much the accessory pigments improve Botryoglossum's ability to absorb all the light that comes its way.  

Morphology  Ecology  Life History  Taxonomy  Reproduction 

© 2001 Shasta Daisy Pistey-Lyhne . All rights reserved.