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Pigments are useful in light trapping and attracting pollinators

Photosynthetic pigments are of prime importance

Pigments are molecules which characteristically reflect light at certain wavelengths which leads to their color. Therefore, they also absorb light energy at critical wavelengths. The most important pigments are those involved with light trapping and energy conversion, as in the photosynthetic process. Chlorophyll and carrier molecules that work together are packed into granules on the internal membranes of chloroplasts. The granules are termed photosynthetic units, and the membranes are termed thylakoids. One way of characterizing the differences between the photosynthetic units is that those with little chlorophyll b are usually typical of photosystem I, while those in which the chlorophyll b is in about equal proportion with chlorophyll a are more typical of photosystem II.

In the illustrations shown here, the bodinier beautyberry exhibits a typical green pigmentation of the leaf blades. The chlorophyll contained is both a and b. The molecular configuration illustrated at the left is of chlorophyll a, but altering the methyl group (shown in red) to an aldehyde (-CHO) would convert the molecule to chlorophyll b. The long phytol tail is embedded in the thylakoid membrane for stability, while the porphyrin ring acts as an antenna to capture photons of light energy. The magnesium atom carries the electrons used in photosynthesis.

Additional pigments such as carotenoids also found in chloroplasts may be responsible for aiding in light trapping by broadening the spectrum of light absorbed and by assisting energy conversion of the photosynthetic units.

Other pigments include anthocyanins, carotenoids and flavonoids. Often the colors and patterns are best recognized by viewing with ultraviolet illumination as in the case of insect vision. Pigments of petals and other floral parts are usually not chlorophylls, and are often highly specialized for the attraction of pollinators, including insects, birds, and small mammals.

 

Left illustration from: Mauseth, 1998, Botany: An Introduction to Plant Biology, 2nd Ed., Jones & Bartlett Publishers

   
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